Age, growth and reproduction period of the grass goby (Zosterisessor ophiocephalus Pallas 1811) in the Bay of lzmir were studied. The age groups ranged from I to V, and mean total lengths of these age groups were 11.7, 14.3, 16.3, 17.7 and 19.9 cm, respectively. The von-Bertalanffy growth parameters were: L-infinity = 27.4 cm, K = 0.169 year(-1) and t(0) = -2.119 year. Generally, weight increased allometrically and the length-weight relationship estimated for all fish was W = 0.0086 x L-3.06 (R-2 = 0.95). The reproduction period began in February and extended until May according to gonadosomatic index values.