[Background] Nitrite is one of the most common pollutants in intensive shrimp aquaculture. In order to provide theoretical basis of nitrite prevention and cure for culture of Macrobrachium rosenbergii, we investigated the toxicity effects of nitrite on M. rosenbergii haemocytes, and the role of antioxidant enzymes in anti-nitrite defense.[Method] Prawns were exposed to different doses (0, 1, 5 and 10 mg·L^-1) of NO₂^--N. Reactive oxygen species (ROS) production in haemocytes and apoptotic haemocyte ratio were determined by flow cytometry. The total haemocyte count (THC) and intracellular antioxidant enzyme activities were also analysed after 0, 6, 12, 24 and 48 h exposure.[Result] Results showed that 1 mg·L^-1 NO₂^--N had no significant effect on ROS production, apoptotic cell ratio and THC. Increase of ROS production and decline of THC could be observed in prawn exposed to 5 mg·L^-1 NO₂^--N after 24 h, and increase of apoptotic ratio occurred after 48 h. Increase of both ROS production and apoptotic ratio were observed in prawn exposed to 10 mg·L^-1 NO₂^--N after 6 h, and THC decreased after 12 h. Superoxide dismutase (SOD), catalase (CAT), and glutathion peroxidase (GPx) activities in haemocytes were induced by NO₂^--N to different levels.[Conclusion and significance] These results clearly demonstrate the dose-and time-dependent toxic effect of nitrite. They also indicate that nitrite could induce the ROS generation in prawn haemocytes and then the overproduction of ROS causeing haemocyte apoptosis and subsequent THC decline. This process of oxidative stress is one of the cytotoxicity mechanisms of nitrite on M. rosenbergii. The induced activities of antioxidant enzymes indicate that these antioxidant enzymes play a vital role in anti-nitrite defence.