Abstract: Four heterocyclic glutarimide antibiotics,namely cycloheximide (1), iso-cycloheximide (2),4-［2′-(3″(S),5″(S)-3″,5″-dimethyl-2″-oxocyclohexylidene) ethyl］piperidine-2,6-dione (3),and 4-［2′-(3″(R),5″(S)-3″,5″-dimethyl-2″-oxocyclohexylidene) ethyl］piperidine-2,6-dione (4),were isolated from the endophytic actinomycete Streptomyces sp.KIB-271.Their structures were identified through mass spectrometry and NMR experiments.Among them,compound 4 was reported for the first time as a natural product.In the antimicrobial experiments，1 exhibited obvious antifungal activity in vitro against most of the tested fungus,and was considered as one of the main antimicrobial constituent from Streptomyces sp.KIB-271.

Key words: endophyte, secondary metabolites, spectrometry, antimicrobial