Abstract: The oxygen consumption, CO₂ production and ammonia-N excretion were measured for the parent prawn, Penaeus orientalis under their non-feeding and resting conditions. The repiratory quotient, the ratio of oxygen to nitrogen and metabolic substrate ratio were used to describe substrate metabolism of the prawn. Experiment indicated that oxidation of protein dominated energy metabolism, while lipid was the second source of the energy metabolism. Oxygen consumption was negatively correlated with body weight of prawn, but it increased with development of ovary.