Four new cyclic lipopeptides, cyclo-(AFA-Ser-Gln-Asn-Tyr-Asn-Ser-Thr), named cyclodysidins A–D, were isolated from the broth culture of Streptomyces strain RV15 associated with the marine sponge Dysidea tupha. The sequences of the amino acid building blocks in the compounds and their structures were determined by 1D- and 2D-NMR techniques and CID-MS/MS experiments. The absolute configurations of all a-amino acids were determined by HPLC analysis after derivatization with Marfey's reagent and comparison with commercially available reference samples, while those two of the b-amino fatty acids were determined by using racemic and enantiopure reference samples synthetically prepared.