A series of aaptamines, including one new alkaloid (1), were isolated from the marine sponge Aaptos sp. collected in Vietnamese waters. The structure of 1 was elucidated using NMR and HRESIMS, as well as by chemical transformation of 1 to the previously known aaptamine and established as 3-N-morpholinyl-9-demethyl(oxy)aaptamine. The isolated compounds showed a potential cancer preventive activity.