A new species of the genus Robertus Pickard-Cambridge, Robertus subtilis n. sp. is described from Mt. Odae in Gangwon Province, Korea. Theridion serpatusum Guan and Zhu, 1993 and Lathys annulata Bösenberg and Strand, 1906 are reported for the first time in Korea. Habitus photos and illustrations of these three species are provided.