Phosphorus (P) deficiency is thought to exacerbate the arsenic (As) phytotoxicity in paddy rice. Therefore, experiments were conducted to investigate the effects of extal phosphate supply on As accumulation in and toxicity to rice plants under phosphate deficiency conditions. Rice seedlings being pretreated with -P (phosphorus deficiency) nutrient solution for 14 d accumulated more As than those pretreated with +P (normal phosphorus supply) nutrient solution. -P pretreated rice showed As toxicity symptoms after being exposed to 50 μmol/L arsenate for 4 h, while +P rice did not show any toxicity symptoms. Arsenic toxicity symptoms can be alleviated with increasing of extal P concentrations. Arsenate uptake rate and accumulation corresponded with As toxicity in rice plants. Arsenic concentrations in rice roots decreased with increasing extal phosphate concentrations. The lowest As accumulation and the highest P accumulation were found when the extal P concentration reached 100 μmol/L. In a summary, P deficiency increased the sensitivity of rice to arsenate and increasing of extal phosphate supply could alleviate As toxicity.