Papers 1 - 3) on the biologically active substances contained in the mushroom, Hericium erinaceum (Yamabushitake in Japanese), have been published. During the course of our screening program for pollen growth regulators among the extracts of mushrooms, it was found that one mushroom, Hericium erinaceum, contained a new biologically active substance which we have named hericerin (1). In this paper, we describe the isolation and structural determination of 1 together with an inhibitory effect on pine pollen germination and tea pollen growth.