The mean fiber length of three beech trees (Fagus orientalis L.) at the lower and higher points (1% and 75% tree height) of the stem at an intermediate altitude (500-1000m) in the Caspian forests in Sari region were 1.36 and 1.22mm respectively, close to the values in three trees at high altitude (1000-1500m), that were found to be 1.39 and 1.36 mm. The mean fiber lengths of the whole stem, using stem formula, were considered as 1.31 and 1.38mm at intermediate and high altitudes and so were very close each other. JUVENILE WOOD portions in the stem comprised 17 annual rings, which took up 7.3% of the stem by volume at intermediate altitude. At high altitude, these values were obtained as 18 annual growth rings, and 8.75% JUVENILE WOOD in the stem. The reason for greater JUVENILE WOOD at high altitude was somehow a wider ring width at higher elevation. The mean ring width of lower and upper points of the stem at intermediate altitude were found to be 1.82 and 2.95mm respectively; meanwhile, at high altitude, the findings were 2.97, 3.37mm. Despite the data obtained, t- test comparison was conducted between mean fiber lengths of the two heights of the stems at two altitudes, and no significant differences were found at the 1% level. The exploitation age was strongly dependent on how much JUVENILE WOOD there was in the stems, that at high altitude was greater than at intermediate. However, statistical comparison showed no significant differences between that and the 1% level. Therefore, altitude in the range of about 500m showed no important impact on beech fiber length, exploitation age or JUVENILE WOOD border in Caspian forests.