This study was conducted to determine fish composition and diversity Index in Lake Kalgwai Jigawa State, Nigeria between July 2012 and April 2013. The ichthyofauna of Lake Kalgwai was assessed using catches statistics at three major landing sites of the Lake, namely Marke, Dingare and Kalgwai. Twenty-seven fish species belonging to sixteen families were encountered during the study period. Fish species of Cichlidae, Bagridae, and Mormyridae were found dominant representing 13.8%, 13.4% and 12.6% of the total catch, respectively. Citharinidae was the least abundant (0.53%). Eight species were found numerically dominant in the catch based on the monthly generated data. It include Lates niloticus (11.1%), Oreochromis niloticus (11.1%), Mormyrus macrophthalmus (9.8%), Synodontis nigrita (8.4%), Bagrus bayad (8.4%), Heterotis niloticus (7.6%), Malapterurus electricus (7.5%%), and Clarias gariepinus (7.0%). Fish diversity indices estimated included species richness (d) which ranged from 0.94 (March) to 1.93 (October), Shannon – Wiener index (H’) between 0.22 (January) to 1.60 (July), Equitability Index (J) ranging from 0.10 in January to 0.89 in July, Simpson’s Index (D) from 0.14 (October) to 0.23 (July) and Species Heterogeneity (1 – D) from 0.77 (September) to 0.86 (October). It was concluded that there was high fish species richness in the Lake. Also, species equitability index of fishes across all the landing sites reveals that the distribution of species or fish population is nearly even.