The present invention relates to a composition comprising an inhibitor of the expression or activity of SH3 domain containing ring finger 2 (SH3RF2) for preventing or treating cancers. More specifically, since the SH3RF2 protein, of which the expression level increases in various cancer tissues, binds to PAK4, which is a cancer-associated gene, to regulate an apoptosis inhibitory function of the PAK4 protein by ubiquitination activity of SH3RF2 RING domain, cancer cells, in which the expression of SH3RF2 is inhibited, sensitively respond to the induction of apoptosis to promote apoptosis and reduce in vivo tumorigenicity, such that the inhibitor of the expression or activity of SHRF2 can be useful as a composition for preventing or treating cancers.