Length-weight relationship is used in morphometric inter-specific and intra-specific population comparisons to assess index of well-being of the fish populace. The Total length (cm) of each fish was taken from the tip of the mouth to the extended tip of the caudal fin using a measuring ruler to the nearest 0.1 cm. Standard length (cm) for each fish was taken as measurement from the tip of the mouth to the caudal peduncle to the nearest 0.1 cm. The total body weight in grams was measured for each fish species to the nearest 0.01 g using a top loading Mettler balance. A total of 92 species of Oreochromis niloticus were sampled for this study, (49 males and 43 females). The standard length (cm) and weight (g) for Males ranges from 17.0-28.3cm/47.34-157.05g, Females ranges from 16.8-31.6cm /92.98-153.7g. Combined sex ranges from 16.8-31.6 cm/47.34-157.05g, a regression coefficient of 0.55, 0.92 and 0.75 respectively. The condition factor of males ranged from 0.58-4.68 (mean value of K=1.72± 1.03) females ranged from 0.47-4.68 (mean value of K=1.25±1.05) while combined sexes has the range of 0.52-4.05 (mean value of K=1.50±1.06). This study provides the first basic and baseline information on Length-Weight Relationship as well as the condition factor of O. niloticus in Kiri reservoir, which would be beneficial to fishery biologist and conservation biologist, for successful development, management, production and ultimate conservation of these fish species

Keywords: Length-Weight Relationship, Condition Factor, Oreochromis niloticus, Kiri Reservoir