Population characteristics such as population structure, growth, mortality, and size at sexual maturity of the Astacus leptodactylus were examined in various lakes based on size-frequency distribution by using FISAT software program from April 2002 to March 2003 in Turkey. Specimens were collected monthly using with fyke-nets of 32 mm mesh size. Population size based on size-frequency distribution between female and male and between two years data were described. Malesoutnumbered females in all lakes and the average sex ratios (male/female) were found to be significantly different. Mean total length (TL mm) was found similar for male and female crayfish in all lakes. However, while the total length of the samples from Iznik was the largest (26-68.5 mm TL),thesamples from Ulubat it was the smallest (15.2-82.3 TL), where as the population from Manyas Lake was intermediate (23 mm-71.5 mm TL). Growth parameter was estimated by using the modified von Bertalanffy growth function for male and female. Growth was continuous throughout the year. Female crayfish were larger and grew faster than males at the same age. In addition, total mortality based on the seasonalized length-converted catch curve for both sexes were Z= 1.87, (female), Z= 1.52, (male) in lake Manyas, Z= 1.78, (female), Z= 1.69, (male), in lake Ulubat; and Z= 1.79, (female), Z= 1.78, (male) in lake Iznik. Exploitation rate between female and male were calculated in lakes Manyas,Ulubat, and İznik as E= 0.57, (female), E= 0.54, (male) E= 0.63, (female), E= 0.57, (male) E= 0.66, (female), E= 0.53, (male), respectively.