To investigate the characteristics of hybrid eggs and larva produced by olive flounder Paralichthys olivaceus females and starry flounder Platichthys stellatus males, we examined the developmental speed of hybrid eggs at different water temperatures. The developmental speed of hybrid eggs tended to increase with increasing water temperature. Specifically, the hatching times were 91 hrs, 62 hrs and 43 hrs at $10^{circ}C$, $15^{circ}C$ and $20^{circ}C$, respectively. The mean biological minimum temperature of the hybrid was $1.3^{circ}C$, which is in between that of the olive flounder and the starry flounder. In high water temperatureseasons, slower growth was observed in hybrids of the starry flounder which is a coldwater fish.