The study was conducted on fetuses in 3, 4 and 5 months of gestation, newly born lambs up to one month age and adult Iranian sheep of Mehraban breed up to 4 years old. All the 5 groups contained 6 animals in each group. The trend of variations in the total length of vertebral column by aging as well as the trend of regional and segmental developmental changes was observed. The total length of vertebral column was 202.8±16.19 mm in 3 month fetus, 294±22.89 mm in 4 month fetus, 405.2±37.28 mm in 5 months fetus, 566.3±30.61 mm in newly born lamb and 1054±87.27 mm in adult sheep. The length of thoracic (1) vertebral column was maximum in the animals of all age groups followed by cervical(C), lumbar (L), coccygeal (Co) and sacral (8) ones, except in 5 months fetus where the length of coccygeal vertebral column was longer than that of the lumbar region. The seresults further indicated that in the cervical region, C2 vertebra was the longest and C1 the shortest in all the age groups. In thoracic region, T1 was longest in 3 and 4 months fetuses, whereas in rest of the animals T13 was longest. The shortest vertebrae in this region were T7 , T8, T5 and T6 in 3 , 4 and 5 months fetuses, respectively, and T7 in newly born lamb and adult sheep. In lumbar region L6 vertebra was longest in most of the age groups except in adult sheep where L5 was longest. In addition to L4 and L5 were also long in 3 months fetus. However, the shortest vertebra was L1 in all stages. In sacral region, S1 vertebra was longest in all age groups, whereas S4 was shortest except in adult sheep where S4 was shortest.