Reproductive behavior of the freshwater prawn,Macrobrachium rosenbergii,which is native to the Pusur River in Chalna County,Khulna Division,Bangladesh,was observed from Jun to Sept,2007.Time-lapse video was used to record typical behavior throughout the reproduction period.The reproductive process described in this paper was definitively referred to the duration from the time of encounter and recognition between two sexes to egg-carrying of the female respectively under the given conditions.Males with 80.0 g plus body weight and the females with 40.0 g plus body weight,the individuals used in this observation were caught from the lower reaches of the Pusur River,then were acclimated in the pools for 15 days outside the riverbank and fresh escargots meat,Viviparus iaiopoma,were provided as food.After acclimation,males above 80 g and female above 40 g were selected and moved into the indoor concrete tanks with a density of one reproductive pair/m2(RP,defined as one male and one female) for further observation.A typical successive process included following incidents:encountering and recognizing between the sexes,male occupying territory,female molting,male seizing a receptive female and performing precopulatory guard,copulating and transmitting its spermatophore to the female,postcopulatory guard and releasing the female,female spawning and carrying eggs.Mate-guard is the main mating tactics for the success of reproduction.