The white sport virus (WSSV) infection level in the nauplius of tiger shrimp, Penaeus monodon was involved with the variation of water conditions. All nauplius were infected with WSSV at all experimental temperatures, and the viral replication may also be influenced by temperature. At the optimal range of temperature (26-31 oC), the WSSV infection levels was increased as the temperature increased. However, the replication of virus in host was suppressed at the above temperature higher than optimal range. In addition, the WSSV infection level in nauplius was accelerated as the increase of nitrite-N concentration in water when nauplius was exposed to the ambient nitrite-N lower than sublethal concentration of 4.9 mg/l.