Effects of some environmental factors (aspect and slope gradient) on improvement of qualitative conditions (stem form and vitality) of pinus eldarica Medw. was investigated in an urban green space of Tehran (Lavizan Forest Park). For this purpose, some quadrangular sample plots of 2.56 Ar were chosen at main geographical aspects and 0-15% and 20-40% slopes. The results present that contrary to stem form, vitality is influenced by aspect and slope gradient (P<0.05). The greatest frequency of vitality quality with grades of 1 and 2, without considering the slope gradient, are found respectively in southern and eastern aspect, and without considering the aspect are presented respectively in 0-15% and 20-40% slopes. From this research, it can be deduced that these environmental factors (aspect, slope gradient) only influence on vitality, whereas, as a whole, tree growth is more vital on slope gradient of 0-15% and southern and or eastern aspect than on other slope gradient and aspects.