Four new purine alkaloids, namely, 6-(1'-purine-6',8'-dionyl)suberosanone ( 1), 3,9-(2-imino-1-methyl-4-imidazolidinone-5-yl)isopropenylpurine-6,8-dione ( 2), 1-(3'-carbonylbutyl)purine-6,8-dione ( 3), and 9-(3'-carbonylbutyl)purine-6,8-dione ( 4), together with three known compounds, guanosine ( 5), thymidine ( 6), and adenosine ( 7), were isolated from the EtOH/CH 2Cl 2 extracts of the South China Sea gorgonian Subergorgia suberosa. The structures of 1- 4 were determined on the basis of extensive spectroscopic analysis, including 1D and 2D NMR data. Compounds 1- 4 all showed weak cytotoxicity toward human cancer cell lines MDA-MB-231 and A435.