The objective of this study was to determine the placentome development during pregnancy and the correlation between placentome diameter and gestational age using transabdominal and transrectal ultrasonography in ewes. A B-mode, linear array, ultrasonography with 5,0-7,5 MHz rectal transducer was used in this study. Examinations were commenced at days 26 to 28 post mating. In this study, fifty pregnant ewes were used. Ultrasonographic examination was performed weekly until birth. Diameters of five placentomes were measured in weekly examinations and then mean diameter was calculated. Among the fifty pregnant ewes, 44 had single pregnancy while six ewes had twin pregnancy. Placentomes were seen since 4th week of pregnancy. Placentomes developed fast in the first weeks of pregnancy and reached maximum diameter in 11th week (3,41±0,04 cm). Diameterof placentomes increased during the firstweeks of pregnancy but decreased in the second half and decreased to 1,73±0,18 cm before birth. A weak correlation was found between gestational age and diameter of placentome in ewes (regression coefficient, r = 0,540). There was no difference between placentome diameters between single and twin pregnancies (P > 0,05). As a result, placentome development in ewes during pregnancy can easily be determined from 4th week of gestation to birth. Besides, because of weak correlation between placentome diameter and gestational age in ewes, it is concluded that, gestational age cannot be determined from diameterof placentome.