Abstract: We conducted a static bioassay test to investigate the acute toxicity of compound trichloroisocyanuric acid to larvae of Penaeus semisuicatus. The concentration of TCCA in the experiment for nauplius and zoea is 0 mgL-1, 0.5 mgL-1, 1.0 mgL-1, 1.5 mgL-1, 2.0 mgL-1, 2.5 mgL-1 and 3.0 mgL-1; that for mysis and post larvae is 0 mgL-1, 1.0 mgL-1, 1.5 mgL-1, 2.0 mgL-1, 2.5 mgL-1, 3.0 mgL-1, 3.5 mgL-1 and 4.0 mgL-1; each concentration has 3 replicates. The results show that the 24 h LC50 and 48 h LC50 with 95% confidence interval for nauplius are 1.47~1.78 mgL-1 and 1.34~1.46 mgL-1, respectively；those for zoea are1.67~1.78 mgL-1 and 1.23~1.36 mgL-1, respectively; those for mysis are 2.05~2.25 mgL-1 and 1.58~1.79 mgL-1, respectively; those for post larvae are 3.14~3.38 mgL-1 and 2.59~2.78 mgL-1, respectively. The safe concentration (SC) for nauplius, zoea, mysis and post larvae is 0.30 mgL-1, 0.22 mgL-1, 0.34 mgL-1 and 0.55 mgL-1, respectively. The results provide references for safe medication in larvae rearing for P.semisuicatus.