<p>Reproductive strategies should be reflected in the genital organs of cetaceans; however, comprehensive comparative studies on male genital organs in cetaceans are limited. This study aimed to investigate the structural characteristics of male genital organs in four small-toothed whale species: short-finned pilot whales, Risso’s dolphins and striped dolphins (family Delphinidae), and narrow-ridged finless porpoises (family Phocoenidae). Macroscopic anatomical and histological examinations reveal commonalities, including an S-shaped curved penis covered by a dense tunica albuginea, a corpus cavernosum penis made of thick fibrous tissue, a retractor penis muscle, and a prostate gland—the sole accessory genital gland—enclosed in thick muscular tissue. Unique to two Globicephalinae species, including short-finned pilot whales and Risso’s dolphins, is an elongated structure at the penile tip that lacks the corpus cavernosum penis, a feature absent in striped dolphins and narrow-ridged finless porpoises. On the basis of these genital characteristics and social structures, the two Globicephalinae species appear to prioritize sperm competition more than striped dolphins. Further research is necessary to elucidate the reproductive strategies of narrow-ridged finless porpoises.</p>