As part of our continuing search for biologically active secondary metabolites from ascidians, we report the structures of four new tetracyclic pyridoacridine alkaloids, styelsamines A-D (3, 5-7), from the Indonesian ascidian Eusynstyela latericius. The cytotoxic ethanolic extract was fractionated via C18 flash chromatography and Sephadex LH-20 gel filtration, yielding the alkaloids as trifluoroacetate salts or free bases. Their structures were elucidated using HRFAB mass spectrometry and multinuclear NMR techniques (COSY, ROESY, HMQC, HMBC), with key HMBC correlations confirming side-chain positions. Styelsamine A (3) racemized and converted to pyridoacridone alkaloid 4 upon storage. Styelsamine B (5) bears an N-acetyl-1,2-disubstituted ethylamine moiety, styelsamine C (6) has a C-9 aldehyde group, and styelsamine D (7) is the deacetyl analog of B. All four compounds exhibited mild cytotoxicity against the human colon tumor cell line HCT-116, with IC50 values of 33, 89, 2.6, and 1.6 µM for 3, 5, 6, and 7, respectively.