Two new caprolactams have been isolated from an unidentified Gram-positive bacterium obtained from a deep-ocean sediment sample. Caprolactins A (1) and B (2), which were obtained as an inseparable mixture, are composed of cyclic-L-lysine linked to 7-methyloctanoic acid and 6-methyloctanoic acid, respectively. The structures were proposed using spectroscopic methods and confirmed by synthesis. Both caprolactins A and B are cytotoxic towards human epidermoid carcinoma (KB) cells and human colorectal adenocarcinoma (LoVo) cells with MIC values of 10 and 5 μg/mL, respectively, and exhibit antiviral activity towards Herpes simplex type II virus at a concentration of 100 μg/mL.