Information on the dietary phosphorus (P) requirement is essential in the formulation of a cost-effective and low-pollutant feed. Ten isonitrogenous (40% CP) casein–gelatin-based diets containing five graded levels of P (0, 0.5, 1, 1.5, 2%) for each of two levels of calcium (Ca) (0, 1.5%) were fed to juvenile Penaeus monodon previously fed a basal diet containing no P and Ca for 15 days. After 90 days, survival ranged from 70% to 87% but was not significantly different (P<0.05) among treatments. A significant Ca and P interaction was obtained in percent weight gain. Shrimp fed with diet containing 0.5% supplemental P (0.74% total P) without Ca supplementation showed a significantly higher weight gain. For total biomass of shrimp, analysis of variance showed no significant interaction between Ca and P level, but significant differences were obtained among P levels when averaged over two Ca levels. The graded levels of P did not affect shrimp whole body P (1.07–1.13%). Whole body P was not a good index in determining the P requirement of P. monodon. In the absence of Ca, 0.5% supplemental P (0.74% total P) provided maximum growth of P. monodon postlarvae. The level of Ca should be reduced in formulating diets to minimize supplemental P, thereby effecting savings in feed cost and less loss of P to the water system.