The paper deals with the effect of ammonia-nitrogen (NH 3-N t) and nitrite-nitrogen (NO - 2-N) in the nursery water on the larvae of Macrobrachium rosenbergii , in which the concentrations of NH 3-N t and NO - 2-N were tested. The result showed: when the concentration of ionized ammonia(NH 3-N m) exceeded to 0 11 mg/L over 6 days, larval metamorphosis would be delayed causing heavy larval mortality. Daily change in the concentration of NH 3-N t and NO - 2-N was irregular, but the concentration of NH 3-N t and NO - 2-N tended to increase gradually during nursery period.