Two isothiocyanates, epipolasin-A 1 and-B 2, and two corresponding thiourea derivatives, epipolasinthiourea-A 14 and-B 15, were isolated from the marine sponge E. kushimotoensis. Their structures were elucidated on the basis of chemical and spectral evidence. The thioureas 14 and 15 showed cell growth inhibition activity.