Specimens belonging to the genera Mycena and Collybia which have been preserved in the herbarium of National Institute of Agricultural Sciences and Technology, Suwon, Korea were investigated. Among them, four species were confirmed to be Hydropus species viz Hydropus marginellus, H. nitrata, H. erinensis, and H. floccipes. Authors registered them to the Korean mycoflora with full descriptions, illustrations and Korean names.