Pseudostellaria longipedicellata S. Lee, K. Heo & S. C. Kim is newly described from the Taebaek Mountain Range across three eastern provinces (i.e., Gangwon, Chungcheongbuk, and Gyeongsangbuk) of the Korean Peninsula. Pseudostellaria longipedicellata is similar to P. palibiniana (Takeda) Ohwi by having an open flower, glabrous pedicel, and slender taproots, but differs by its shorter, decumbent, and slender stems, oblanceolate leaves distally changing to elliptic or narrowly ovate, and the fertile pedicel that elongates to the ground when bearing fruit. A dichotomous key to the Korean species of Pseudostellaria Pax is provided in this paper. Also discussed are the major differences of P. longipedicellata from its congeners, and the new species' possible pollination and dispersal mechanisms.