Marine microorganisms are widely recognized as rich sources of secondary metabolites. These organisms, flourishing in diverse marine environments, have produced a wide variety of structurally unique and biologicallly active compounds that have attracted considerable attention for biomedical studies. During the course of our search for novel natural products from marine bacteria, two cyclic tetrapeptide(1 and 2) are isolated from the culture broth of an actinomycete from the sediment collected from Gageo-Do, Korea. The structures of these compounds were determined to be cyclo-(L-val-L-pro-L-val-L-pro) (1) and cyclo-(L-leu-L-pro-L-leu-L-pro) (2) on the basis of combined chemical and spectral methods.