A new antibiotic, cyanocycline A, was isolated from the fermentation broth of Streptomyces flavogriseus strain No. 49, a soil isolate. The molecular formula of cyanocycline A was determined to be C22H26N4O5. The antibiotic has a cyano group and a N-heterocyclic quinone moiety in its structure. Cyanocycline A was found to have broad spectrum antimicrobial and antitumor activity.