This paper deals with the toxic effects of NO2 - N and NH3 - N on Macrobrachium rosenbergii larva. The 24h, 48h, 72h, and 96h LC50 values of NO2-N and NH3-N for Z5, Z7 and Z9 were obstained. The safe concentrations of No-2-N and NH3-Nt (NH3-Nm) for Z5, Z7 and Z9 were 0. 64, 1. 38, 1. 68mg/L and 2. 04(0. 287), 2. 26(0. 318),2. 55 (0. 358)mg/L respectively. The Larva of Z7 and Z5 poisoned subacutely for 12-day showed that the larval developement, metaborphosis and survival rate decreased with the concentration. The toxic effects of the toxicant strengthen obviously when the toxicant concentration exceeded the safe concentration.