Abstract: The toxicity data of 22 representative aquatic organisms were collected from the laboratory toxicity tests, authoritative toxicity databases and published in literature following principles of accuracy, relevance and reliability. The aquatic life criteria (ALC) for malathion in the Yangtze River Delta Region were derived by Species Sensitivity Distributions (SSDs) and Toxicity Percentile Rank (TPR) respectively. The results show that the acute and chronic ALCs of malathion derived by SSD were 0.865 5 and 0.036 2 μg·L^-1, respectively; the acute and chronic ALCs of malathion derived by TPR were 0.400 0 and 0.033 4 μg·L^-1, respectively. The final criteria derived by TPR were recommended as ALCs for malathion to protect aquatic organisms in the Yangtze River Delta Region. In addition, the recommended ALCs for malathion were compared with criteria abroad and existing Chinese water quality standards (WQS). The present research could provide scientific reference for WQS revision and aquatic risk assessment in China.