Seasonal growth pattern and reproductive biology of the Baltic prawn, Palaemon adspersus, were studied in the southern Black Sea between February 2002 and January 2004. The seasonal von Bertalanffy growth parameters, computed from monthly length–frequency distributions, were estimated as L∞ = 62.99 mm TL, K = 1.190 year−1, C = 0.815, and WP = 0.847 for females and as L∞ = 49.63 mm TL, K = 1.085 year−1, C = 0.011, and WP = 0.407 for males. Growth performance index of females (Φ′ = 3.67) was greater than it was for males (Φ′ = 3.43). Based on latitudinal gradients, water temperature negatively affected Φ′ of P. adspersus. Sexual dimorphism in size was evident, females being larger than males. This typically shallow water species was observed in water depths as deep as 30 m. Compared to shallower water depths, larger individuals were observed in deeper water depths. The size at sexual maturity for females (TL50) was estimated as 53.60 mm TL. Ovigerous females were recorded from March to August and juveniles appeared in the benthic population in August. Ovary development was related to photoperiod and occurrence of ovigerous females was linked to increased water temperature.