Upland oak-dominated northern Zagros forests are coppices and almost destroyed. This forests characterized by silvopastoral use and utilization of oak leafs to feed domestic animals. This paper, reports results of a biometrical study carried out in Northern Zagros forests of Iran. The aim of this study was to analyze the forest structure in order to identify specific structural patterns. Data was collected from 319 circular plots (0.1 ha) established in 2003.The study site was classified into four categories according to the geographical directions: (1) Northern Forests (98 plots), (2) Southern Forests (80 plots), (3) Eastern Forests (77 plots) and (4) Western Forests (64 plots). In each plot, all of over 5cm dbh trees (stems ≥5 cm DBH), species, diameter at breast height (i.e. 1.3 m above ground), height and canopy diameter of two trees in each plot (nearest tree to center of plot and the most thickness tree in plot) was recorded. The differences in diameter size, basal area, tree height and canopy area in forest situated in different geographical directions were analyzed using one-way ANOVA. Species composition in different geographical directions was compared by chi-square test. Average height, diameter, and canopy area of dominant trees were compared by T-test. Results show, that, difference of trees combination between different geographical directions is significant)p< 0.01). While, there is no distinction between eastern and western forests. The comparison of average diameter of main tree species shows, that there is distinction between him (p< 0.01). The major part of trees (77.9%) belongs to natural diameter classes (NDC) 0.6-1.8. The average of basal area in studied forests makes 14.02 m2 /ha. Maximum and minimum of basal area in investigated forest were 15.69m2 /ha (in northern slopes) and 11.96 m2 /ha (in southern slops) respectively. The average of tree number in these forest stands was 337 trees/ ha, in northern forest stands — 411 trees/ha, in souther
