Population structure and growth of Mossul bleak, Alburnus mossulensis, a native species of cyprinids in Bibi-Sayyedan River of Semirom, Isfahan, were investigated by monthly sampling during December 2010 to December 2011. For this purpose, 543 speciments (353 females, 159 males and 31 immature) were caught using seine net (5 mm mesh size) and a cast net. Age groups of males and females were 0+ to 5+. The most frequent age group was 2+ in both sexes. The sex ratio was 1M:2.2F (p < /em><0.01). Males outnumbered the females in younger age classes and females outnumbered the males in older age groups. The highest condition factor was observed in April for males and in March for females. The mean condition factor (CF) was not significantly different between the sexes among all fish during different months (p < /em>>0.05). The largest female was 16.80 cm in total length and 49.12 g in weight, while the largest male was 14.10 cm in total length and 28.19 g in body weight. The length-weight relationship was calculated as W = 0.0169L3.0355 (r2=0.95) for males, W=0.0061L 3.1751 (r2=0.98) for females and W=0.0066L3.139 (r2=0.99) for all fish (males, females and immature). Regression coefficient (b) based on Pauly test, was significantly different from 3 in females, but not in males (p < /em><0.05), indicating an isometric growth pattern in males and a positive allometric growth pattern in females and all fish.