The population structure and biological aspects of the shallow water mysid Mesopodopsis orientalis were studied in the Versova mangrove, Mumbai, India. The monthly collections ranged from 0-2104 ind.m sup (-3)with an average of 78.6 ind.m sup (-3). The sampled population was found in a wide range of temperature (25.5 degree celsius to 34 degree celsius) and salinities (20.3 to 37.1). Carapace length significantly correlated with total body length (P < 0.01). Mesopodopsis orientalis breed throughout the year but there is a seasonal variation in the intensity of breeding. The size of mature males and females was at maximum during the post-monsoon period. The species produced more than one generation per year and the number of embryos carried by a single female ranged from 6-18, and was correlated with female body length (R sup (2) = 0.69). Egg size varied between 0.32 and 0.45 mm, with no correlation with length of females.