Diel rhythm of oxygen consumption (OC) of the starry flounder Platichthys stellatus was measured at different water temperatures in a closed recirculating seawater system with a respiratory chamber. The fish consumed 70.5, 79.7, and 90.6 mg $O_2/kg/hr$ at 15, 20, and $25^{circ}C$, respectively, showing a linear increase in OC with water temperature. The OC of fish showed a clear diel rhythm, with lower values during the day and higher values at night, in accordance with the light (09:00-21:00) and dark (21:00-09:00) phases of the diel cycle (12L:12D) in water at 15 and $20^{circ}C$. However, the OC of the fish showed an unclear diel rhythm with the light and dark phases of the diel cycle at $25^{circ}C$. The respective OC at 15, 20 and $25^{circ}C$ was 63.8, 72.4, and 88.4 mg $O_2/kg/hr$ during the light phases and 77.2, 87.1, and 92.8 mg $O_2/kg/hr$ during the dark phase. The starry flounder is thought to be a nocturnal fish with a higher OC at night, while it rests during the day. Its OC was the most stable in the light, when it did not feed. Consequently, the night-time OC is the active OC and the day-time OC is the resting OC in the starry flounder.