Griseolic acid, a potent inhibitor of cyclic adenosine 3',5'-monophosphate phosphodiesterase, was isolated from the fermentation broth of Streptomyces griseoaurantiacus SANK 63479. Treatment of griseolic acid with HCl-MeOH gave adenine and pseudo-sugar. The structure of griseolic acid, adenine nucleoside type structure, was elucidated by chemical degradation and X-ray analysis, and was shown to be structure 1.