This study was to evaluate the effect of stocking densities on the nitrogen and phosphorus budgets for a polyculture of the crab Portunus trituberculatus and the Pacific white shrimp Litopenaeus vannamei. The shrimps (initial weight, 0.012 g) were cultured at a density of 45 shrimp m–2, and juvenile crabs (initial weight, 0.024 g) were cultured at five densities of 0, 3, 6, 9, and 12 crabs m–2. The treatments were grouped as C0S45, C3S45, C6S45, C9S45, and C12S45, respectively. Water quality parameters, growth of shrimp and crabs, and nitrogen and phosphorus budget were measured. The results indicated that the shrimp performances in polyculture treatments C3S45 and C6S45 were superior to those in the crab-free treatment (C0S45). The crab in treatments C3S45 and C6S45 exhibited a significantly higher final mean weight and carapace width/length than those in treatments C9S45 and C12S45. The final size and survival of crabs had a negative correlation with the increasing crab stocking density. The contents of total phos-phorus and total nitrogen and the comprehensive contamination index values were higher in the C9S45 and C12S45 treatments than in the other treatments. The conversion ratios of nitrogen for crab and shrimp growth in treatment C3S45 were significantly higher than those in the crab-free treatment. These findings indicate that polyculturing shrimp with crabs at suitable densities can improve productivity, profitability, nutrient utilization, and the environmental quality. From the 60-day treatments, the optimal culture densi-ties were 3– 6 crabs m–2 and 45 shrimps m–2.