Polysiphonia senticulosa Harvey (Ceramiales: Rhodophyta) was recorded for the first time in Korea, and its vegetative and tetrasporangial morphologies are described. This species is characterized by the combined features of having a vegetative axial segment with 4 pericentral cells, a main axis without cortication, pseudodichotomous branching, branches with sharply pointed apical cells, flexuous branches hooked backward below, the presence of cicatrigenous branches, axillary endogenous stichidia, and the production of 1-3 tetrasporangia per stichidium. Based on this study, it is distinguished from Polysiphonia morrowii Harvey by its flexuous branches and the number of tetrasporangia produced per stichidium.