In the course of our continuing investigation of the constituents of a hallucinogenic mushroom, Gymnopilus spectabilis (Japanese name, O-waraitake) collected at Oguni, Yamagata, we have isolated novel type of polyisoprenepolyols designated as gymnopilins -A, -B, and gymnoprenols -A, -B, -C, and -D etc. These substances occured as a mixture of some homologues were separated and throughly purified by means of preparative HPLC and their chemical structures were determined on the basis of the results of oxidative degradation as well as their spectroscopic properties. These polyisoprenepolyols were shown to contain same repeated unit corresponding to hydrated form of usual isoprenoid chain, two or three double bonds and a terminal vicinal diol moiety or the corresponding ester with 3-hydroxy-3-methyl-glutaric acid. The location of double bond was confirmed by the degradation studies. The structures of polyisoprenepolyols such as 1a and 2a have never been encountered in natural products obtained so far. The stereochemistry and biological activities are under investigation.