The Caspian goby, Neogobius caspius, belongs to Gobiidae family and it lives only in the Caspian Sea. Since this fish may be used as food for Caspian Sea commercial, fishes therefore this fish can be regarded as an important endemic species. The main aims of this study was studying dietary habits such as food items, preference, quantitative prey and their temporal, spatial and size changes. Sampling has been done monthly from Oct. 2005 to Sep. 2006 in four stations from depth 0-15 meters at Astara to Chaboksar stations, with bottom trawl. (In Gilan coasts in the Caspian Sea waters). The results on 701 full-gut specimens of N. caspius showed that, they have a total length of 24-176 with an average 88.70±31.4 mm, a weight 0.15-65.10 with an average 10.85±11.7 g and an age 0+-6+ with an average 1.96±1.4 years old. Coefficient vacuity, relative gut length and intensity of gut fullness were 8.72%, 0.76±0.17 and 267.7±263.3 respectively. There were significant differences between stations, seasons, sampled depths and the fish ages in studied indexes. Caspian goby was feed on 30 different preys consist of Zooplanktons (8 different groups), Benthic animals (15 different groups) and fishes (7 different groups). Young and yearlings had fed mainly mixed food (zooplankton and small benthic animals) and adults had fed mainly zoobenthose. Gammarids, Bivalvia, Cumaceae and Vormes were observed in 44.7, 38.9, 24.8 and 19.7% of full gut studied samples respectively. Bivalvia, Cumaceae, Gammarids and Ostracoda were main preys and had the most numbers in the fish gut, 26.9, 25.9, 25.3 and 10.9% respectively. In general, it can be concluded that, goby in studied area is euryphagous, carnivorous, benthphagous and mix-eater (molluscs-crustaceans) species.