Al-Jabal Al-Akhdar Mountain is the richest vegetation and highest species diversity in Libya. The aim of the present study was to evaluate the population structure of twelve endangered species in Al-Jabal Al-Akhdar. These species are: Arbutus pavarii Pamp., Cupressus sempervirens L., Ceratonia siliqua L., Juniperus phoenicea L., Laurus nobilis L., Olea europaea L., Pinus halepensis Miller., Pistacia lentiscus L., Querecus coccifera L., Seriphidium herba-alba (Asso) Soják., Thymus capitatus (L.) Hoffmanns. & Link and Ziziphous lotus (L.) Lam. These species collected from downstream, midstream and upstream of Al-Marj-Al-Baida motorway, El-Beida, Jardas Jerrari, Shahat, Sidi Ahmad Al-Hemery, Susah and Wadi El-Kouf in Al-Jabal Al-Akhdar. The size index of each individual was calculated and then used to classify population into seven size classes. The height, mean diameter, height to diameter ratio, size index and volume per individual in each size class were determined. Generally, the height to diameter ratio was more than unity for Arbutus pavarii, Cupressus sempervirens, Ceratonia siliqua, Juniperus phoenicea, Laurus nobilis, Olea europaea, Pinus halepensis and Querecus coccifera, this means that the diameter of these species tend to expand vertically rather than horizontally, while the height to diameter ratio was less than unity for Pistacia lentiscus, Seriphidium herba-alba, Thymus capitatus and Ziziphus lotus. Five forms of size distributions along the different elevations were recognized: more or less inverse J-shaped distribution, positive skewed distribution, bell shaped distribution, more or less J-shaped distribution and more or less stationary size distribution biased to large size.