Erylosides G--J (1--4), four new triterpenoid saponins, were isolated from the sponge Erylus nobilis collected from Jaeju Island, Korea. On the basis of the results of combined chemical and spectral analyses, the structures of the aglycones were determined to be lanostane-based, modified penasterols. The oligosaccharide portions were composed of one unit each of L-arabinose, D-galactose, and 2-N-acetyl-D-glucosamine (1 and 3) or two units of L-arabinose and one unit of 2-N-acetyl-D-glucosamine (2 and 4). These compounds exhibited moderate cytotoxicty against a human leukemia cell line.