It is important to improve the level of production per animal in animal breeding. The improving of the level of fertilizing of the sheep has a great importance in people's nutrition and the contribution of the countrys economy. For this aim, this investigation was done to prove the applicability of the system of lambing in Karacabey Merino sheep three times in two years. The sheep were mated in 8-month intervals consisting of 5-month pregnancy; 2-month lactation and 1-month resting periods. After mating, the fertility traits, survival and growth in the lambs and body weight in ewes before mating were given importance. The effects of age of dam, birth season, sex and birth type of the lambs as the enviromental factors whose effects could be evaluated on the birth weight and weight on the 60th day of the lamb have been investigated. The effects of these factors have been established by means of Least Squares method. It has been found that while fertility traits such as oestrus, pregnancy, partrution, rate of lamb, twinning and litter size were 99.35,90.25,88.96, 137.01, 52.55%, and 1.54% respectively in June; 95.17, 82.75, 78.62, 105.51,34.21%and 1.34% respectively in March, the values of the same fertility traits were 97.69, 80.76, 80.76, 102.31, 26.66% and 1.27% respectively in January. It has been established that there was statistical significant between the fertilazing traits of these three periods (P<0.05, P<0.01). During the investigating, it has been found that the average lambing interval between the first and second lambing was 284 days but between the second and the third 295 days. It has been found that the birth weight and 60th day-weight of male lambs from mating in June were 4.32 and 19.42 kg, the values of the same traits of the female lambs 4.07 and 17.69 kg; the birth weight of the male and female lambs from mating in March was 4.58 and 4.31 kg and 60th day-weight 19.90 and 18.75 kg; the values of the same traits of the male and female ones in January were 5.24 and 4.99 kg, 21.42 and 20.19 kg respectively. That the values of birth weight and the 60th day weight of the male and female lambs from mating in January were statistically different from the values of the same traits of the lambs from mating in the other periods have been found (P<0.001). The survival on 60th day of the lambs, which were born after mating in June, March and January has been established as 91.94 %, 92.15 and 96.99 respectively (P<0.05). The general average values of the body weights of ewe before mating were 68.03, 68.82 kg respectively in mating in June, March and January. It has been found that the birth type, sex and season, which were investigated factors, had significant effects on the birth weight but not the age of dam (P<0.01). That these investigated factors, except season, had significant effect on the 60th day weight has been found (P<0.05, P<0.01). When the research is completely considered, it was concluded that programme of lambing three times in two years would be able to succesfully apply to the Karacabey Merino Sheep.