Genetic variation of nine oriental sweet gum populations was estimated at a common garden test in the optimal distribution area of the species. Open pollinated seeds were collected from 16-27 families for each population. The test was established using randomized complete block design in 25 blocks with single tree plot in 2009. Each block was included, 223 families. While the initial seedling heights were recorded at the establishment time, root collar diameter, height, and the number of branches were measured at the end of growing season for two consecutive years. With respect to seedling traits, the highest elevation population (Bozd) and the northernmost population (Yata) were found to be differentiated from the other populations. On the other hand, the populations from optimal distribution areas appeared in the same group. Variances among populations were higher than variances among families within populations. Q(ST) values were ranged from 0.30 to 0.52 and were equal or lower than F-ST indicating population differentiation is influenced by both genetic drift and natural selection. Individual heritabilities were between 0.07-0.45 and family heritabilities were between 0.31-0.75. The additive genetic coefficients of variation were ranged from 5.8 % to 15.8 % in pooled data from all populations. Individual heritability, family mean heritability and additive genetic coefficient of variation were also estimated for each population. Gunn and Ceti populations which are located in the optimal distribution area of the species have found to possess high genetic diversity within populations. The findings were evaluated for gene conservation.