Psathyrella turcosomarginata is described and illustrated as a new species from Japan (Fukuoka Prefecture, Kyushu). This species is assigned to section Spintrigerae because of its lack of pleurocystidia and basidiome habit. It is characterized by having fairly large basidiomes, a distinct sulcate-striate pileal margin, and cheilocystidia with mucoid deposits that stain bluish green in ammonia solution.