A new potent tyrosinase inhibitory cyclic octapeptide, pseudostellarin G, has been isolated from the roots of Psedostellaria heterophylla and the structure was elucidated by extensive 2D NMR methods and chemical degradation. Recently a number of cyclic peptides with unique structures and biological activities have been isolated from natural origin. As part of our ongoing investigation of bioactive cyclic peptides from higher plants, 1,2) we have isolated a novel cyclic octapeptide, named pseudostellarin G, showing potent tyrosinase and melanin formation inhibitory activities, from the roots of Psedostellaria heterophylla (Caryophyllaceae). Tyrosinase inhibitors may control over production of the dermal melanin pigment since tyrosinase, which is a bifunctional copper protein widely distributed in animals and plants, plays an important role in the process of melanin biosynthesis.3) In this paper, we describe the isolation and structure elucidation of pseudostellarin G (1) and its potent activity of a novel tyrosinase inhibitor.