The first study of biological and ecological characteristics of grass goby, Zosterisessor ophiocephalus (Palllas, 1814) was conducted in the area of Novigrad sea (Adriatic sea). During the research 1229 grass gobies was caught. The total body length was from 4,3 cm to 20 cm (12,30 ± 2,70 cm), and weighted from 0,80 g to 76,96 g (20,11 ± 12,79 g). Male to female ratio was 1,13:1, and it was not significantly differentiated from expected ratio (1:1). The medium value of the total body length of males (13,11 cm) was statistically significantly greater than the medium value of the total body length of females (12,11 cm). Length-weigh growth of grass goby was negative allometric (b=2,920), and the value of estimated condition index was 0,953. Statistically significant differences in the medium valued of morphometric relation of males and females are noted. Based on the shape of urogenital papillae sex dimorphism was noted it both male and female grass gobies. Feeding activity of grass gobies was the highest in spring, and the lowest in winter period. Essential prey was crustaceans and fish. Age was determined by specific reading of otoliths, and the oldest female and male were 5 years old. The growth of the grass goby was described by von Bertalanffy model (L∞=21,14 cm; K=0,351; t0=-1,321; R2=0,890). The spawning period was from February to May, and the largest value of gonadosomatic indeks (GSI) was noted in April. Relative female’s fecundity ranges from 68,33 to 127,52. Low values of total mortality coefficient (Z=0,432), is a consequence of relatively low natural mortality rate (M=0,344), while fishing mortality is insignificant due to the fact that grass goby is not a fishery species. Exploitation rate of the grass goby is still not alarming (E=0,203) for Novigrad sea.