A new nucleosidyl-peptide antibiotic, sansanmycin, was isolated from an unidentified Streptomyces sp SS. The structure of sansanmycin was elucidated by analyses of its alkaline hydrolysate and spectroscopic analyses. Sansanmycin exhibits antibacterial activity against Mycobacterium tuberculosis H(37)Ra and Pseudomonas aeruginosa with MIC values of 10 and 12.5 mug/ml, respectively.