We investigated gamete longevity in two sea urchin species, Echinometra mathaei (Em) and Tripneustes gratilla (Tg), via laboratory experiments. The longevity of dry sperm at different ages (6, 12, 18, 24, and 30 h after collection) was tested at 20°, 25°, and 30°C. Sperm viability was determined by the percent cleavage of eggs after in-vitro fertilization. Dry sperm of Em remained viable longer than dry sperm of Tg at all temperatures. The viability of dilute sperm and eggs was also determined at 20°, 25°, and 30°C over varying durations (for sperm, 5, 45, and 85 min; for eggs, 1, 3, 6, 12, and 24 h). The viability of dilute Em sperm remained relatively constant over time (nearly 100%) at 20° and 25°C, but decreased rapidly at 30°C. The viability of Tg sperm declined gradually over time at 20°C and decreased sharply at 25° and 30°C. Eggs of Em and Tg remained fertilizable for 12 and 6 h, respectively. Most eggs of Em and Tg underwent normal development when exposed for less than 6 h and 3 h, respectively. These results may illuminate the different fertilization strategies of these two sea urchin species.