Three new lamellarin alkaloids, lamellarins gamma (1), alpha (2), and epsilon (3), along with eight known lamellarin alkaloids, lamellarins M (4), K (5), K-diacetate (6), K-triacetate (7), U (8), 1 (9), C-diacetate (10), and X-triacetate (11), have been isolated from the Indian ascidian Didemnum obscurum. The structures of 1-11 were established using standard spectroscopic techniques. The structure of lamellarin K-triacetate (7) was further confirmed by X-ray crystallographic analysis. The antioxidant properties of lamellarin gamma, lamellarin gamma-monoacetate, lamellarins K, U, and I, and lamellarin C-diacetate were evaluated.