Drug development using marine bioresources is limited even though the ocean occupies about 70% of the earth and contains a large number of biological materials. From the screening test of the marine sponge extracts, we found Hyrtios sp. sponge collected from Chuuk island, Micronesia. In this study, the Hyrtios sp. extract was examined for anticancer activity against human colorectal carcinoma RKO cells that are wildtype for p53 and RKO-E6 that are p53 defective. The Hyrtios sp. extract dose-dependently inhibited viability in both cell lines. Multinucleation as an indication of mitotic catastrophe was also observed. Cytotoxicity tests gave significantly different results for RKO and RKO-E6 cells after 48 h exposure to Hyrtios sp. extract. In RKO cells treated with Hyrtios sp. extract, cell death occurred by induction of p53 and p21 proteins. In p53-defective RKO-E6 cells, Hyrtios sp. extract decreased expression of JNK protein and increased p21 protein. These results indicate that Hyrtios sp. extract induced apoptosis via different pathways depending on p53 status and could be a good natural product for developing new anticancer drugs.