In present study, length-weight relationship, length-length relationship and condition factor values were calculated for 11 freshwater fish species of Buyukcekmece Reservoir. Fish specimens were collected by gillnets having different mesh size between March 2009 and February 2010, monthly. The values of the exponent b of the length–weight relationships varied between 2.727±0.020 and 3.381±0.001. The lowest mean condition factor was estimated 0.74±0.08 for C. taenia while the highest value was recorded as 1.72±0.15 in C. gibelio .