- Kabouter (Dutch) – Little people that live underground, in mushrooms, or as house spirits
- Kachina (Hopi and Puebloan) – Nature spirit
- Kahaku (Japanese) – Little people and water spirits
- Kajsa (Scandinavian) – Wind spirit
- Kalakeyas (Hindu) – Descendants of Kala
- Kallikantzaroi (Greek) – Grotesque, malevolent spirit
- Kamaitachi (Japanese) – Wind spirit
- Kamatayan (Philippine) – Philippine counterpart of Death
- Kami (Japanese) – Nature spirit
- Kamikiri (Japanese) – Hair-cutting spirit
- Kanbari-nyūdō (Japanese) – Bathroom spirit
- Kangla Sha (Meitei mythology) – Dragon Lion in the Kangla Palace
- Kanbo (Japanese) – Drought spirit
- Kanedama (Japanese) – Money spirit
- Kappa (Japanese) – Little people and water spirit
- Kapre (Philippine) – Malevolent tree spirit
- Karakoncolos (Bulgarian and Turkish), also in Bosnia and Herzegovina and Serbia known as Karanđoloz – Troublesome spirit
- Karakura (Turkish) – Male night-demon
- Karasu-tengu (Japanese) – Tengu with a bird's bill
- Karkadann (Persian) – One-horned giant animal
- Karkinos (Greek) – Giant crab
- Karura (Japanese) – Eagle-human hybrid
- Karzełek (Polish) – Little people and mine spirits
- Kasa-obake (Japanese) – Animated parasol
- Kasha (Japanese) – Cat-like demon which descends from the sky and carries away corpses
- Kashanbo (Japanese) – Kappa who climb into the mountains for the winter
- Katawa-guruma (Japanese) – Woman riding on a flaming wheel
- Katsura-otoko (Japanese) – Handsome man from the Moon
- Katallan (Albanian) – Man-eating giant
- Kaukas (Lithuanian) – Nature spirit
- Kawa-uso (Japanese) – Supernatural river otter
- Kawa-zaru (Japanese) – Smelly, cowardly water spirit
- Kayeri (Cuiva) - Mushroom-like monster
- Ke'lets (Chukchi mythology) – Ogre or evil spirit
- Keelut (Inuit) – Hairless dog
- Kee-wakw (Abenaki) – Half-human half-animal cannibalistic giant
- Kekkai (Japanese) – Amorphous afterbirth spirit
- Kelpie (Irish and Scottish) – Malevolent water horse
- Ker (Greek) – Female death spirit
- Kesaran-pasaran (Japanese) – Mysterious, white, fluffy creature
- Keukegen (Japanese) – Disease spirit
- Keythong (Heraldic) – Wingless griffin
- Khalkotauroi (Greek) – Bronze-hoofed bulls
- Khyah (Nepalese) – Fat, hairy ape-like creature
- Kigatilik (Inuit) – Night-demon
- Kholomodumo (Sotho) – Gluttonous monster that was one of the first beasts of creation
- Kijimunaa (Japanese) – Tree sprite from Okinawa
- Kijo (Japanese) – She-devil
- Kikimora (Slavic) – Female house spirit
- Killmoulis (English and Scottish) – Ugly, mischievous mill spirit
- Kinnara (Hindu) – Human-bird hybrid
- Kin-u (Japanese) – Bird
- Kirin (Japanese) – Japanese Unicorn
- Kishi (Angola) – Malevolent, two-faced seducer
- Kitsune (Japanese) – Fox spirit
- Kitsune-Tsuki (Japanese) – Person possessed by a fox spirit
- Kiyohime (Japanese) – Woman who transformed into a serpentine demon out of the rage of unrequited love
- Klabautermann (German) – Ship spirit
- Knocker (folklore) (Cornish and Welsh) – Little people and mine spirits
- Knucker (English) – Water dragon
- Kobalos (Greek) – Goblin like thieves and tricksters
- Kobold (German) – Little people and mine or house spirits
- Kodama (Japanese) – Tree spirit
- Kofewalt (Germanic) – House spirit
- Ko-gok (Abenaki) – Hideous monster
- Kokakuchō (Japanese) – Ubume bird
- Komainu (Japanese) – Protective animal
- Konaki-jiji (Japanese) – Infant that cries until it is picked up, then increases its weight and crushes its victim
- Konoha-tengu (Japanese) – Bird-like creature
- Konrul (Turkic) – Bird that is reborn
- Kostej
- Koro-pok-guru (Ainu) – Little people
- Korrigan (Breton) – Little people and nature spirits
- Koto-furunushi (Japanese) – Animated koto
- Kraken (Scandinavian) – Sea monster
- Krasnoludek (Slavic) – Little people nature spirits
- Krasue (Southeast Asian) – Vampiric, floating head
- Krampus (Germany) – Christmas Devil who punishes badly-behaved children
- Kting Voar (Southeast Asian) – Snake eating cattle
- Kuarahy Jára (Guaraní) – Forest spirit
- Kubikajiri (Japanese) – Female corpse-chewing graveyard spirit
- Kuchisake-onna (Japanese) – Vengeful ghost of a woman mutilated by her husband
- Kuda-gitsune (Japanese) – Miniature fox spirit
- Kudan (Japanese) – Human-faced calf which predicts a calamity before dying
- Kui (Chinese) – One-legged monster
- Kujata (Arabian) – Cosmic bull
- Kukudhi (Albanian) – Female demon who spreads sickness
- Kukwes (Mi'kmaq) – Large, hairy, greedy, human-eating bipedal monsters whose scream can kill
- Kulshedra (Albanian) – Drought-causing dragon
- Kumakatok (Philippine) – Death spirits
- Kumiho (Korean) – Fox spirit
- Kun (Chinese) – Giant fish
- Kupua (Hawaiian) – Shapeshifting tricksters
- Kurabokko (Japanese) – Guardian spirit of a warehouse
- Kurage-no-hinotama (Japanese) – Jellyfish which floats through the air as a fireball
- Kurma (Hindu mythology) – Second avatar of Vishnu in the form of a Turtle
- Kurupi (Guaraní) – Wild man and fertility spirit
- Kushtaka (Tlingit) – Shapeshifting "land otter man"
- Kye-ryong (Korean) – Chicken-lizard hybrid
- Kyourinrin (Japanese) – Animated scroll or paper
- Kyūbi-no-kitsune (Japanese) – Nine-tailed fox
- Kyūketsuki (Japanese) – Vampire king