Abstract: Forest structure is an essential key to successful and sustainable poor forest restoration. The study was conducted in Kon Ka Kinh National Park, Gia Lai, Vietnam. Ten plots were made in secondary and also ten plots in old-growth forests. Research results have shown that the secondary forest had a greater density, but the tree sizes are smaller than that of old-growth forests. The Beta fits best to the diameter frequency distribution in the secondary forests, while the Johnson fits best in the old-growth forests. The results for the height frequency distribution were the opposite. The Quadratic model was the best function to describe the relationship between diameter and height in the secondary forests. In old-growth forests, the Ratskowky model was the best model. The spatial distribution of trees was random in secondary forests, but regular in old-growth forests. Richness of secondary forests was bigger, while other indices were lower than those of old-growth forests. Tree quality classes had strong association with species. Findings of the study are good bases for poor secondary forest restoration in the Park.