Three natural stands of beech (Fagus orientalis Lipsky) at different parts of Caspian Forests of Iran (Kelardasht, Sangdeh and Gorgan) were chosen to determine their seeding cycle by stem analysis. For this reason, 85 dominant trees were selected randomly from the stands. After measuring the tree's quantitative and qualitative properties and sampling soil and vegetation from the stands, the dominant trees were fallen down. A disc (20 cm thick) was removed from base of each fallen tree (cross cut), in order to study the annual rings at two directions, particularly annual diameter increment. After analyzing the data, the results were as follows: 1- Two types of seeding were determined for F. orientalis at the three sites: heavy and light seeding. 2- Seeding started at age of 30 to 35 year when seed production is often light.3- Based on the sites characteristics, the heavy seeding started at age of 60 and extended to ago of 75 year.4- The trees had different seeding characteristics due to their different site characteristics and their different performance.5- The light and heavy seeding cycles repeats every 1-3 and 3-9 years, respectively. The difference between the sites was not significant.6- Natural regeneration of beech is more correlated to light seedling cycle will be due to its more frequency than the heavy seeding cycle.7- There were three kinds of relationship between annual diameter increment and seeding cycles as follows:a- If the annual diameter increment is less than 0.74 mm, no seeding cycle will be expected.b- If the annual diameter increment is between 0.74-1.5 mm, light seeding will be expected, but if its diameter increment is more than 1.5 mm, heavy seeding will be expected.