Tortrix viridana L. is the most important pest of oak trees in Iran. The larvae of the pest impose high economic damages because of feeding on the leaves and buds of oak trees and leaving heavy destructions on the invaded trees. To determine the biological characteristics and also the rate of the infestation with this pest, random sampling was performed from 30 trees of Quercus infectoria, Q. libani and Q. brantii and four branches from 4 cardinal sides, each of 50 cm length were cut off as units for the enumeration of green oak moth larvae (or pupa) and after counting the larvae, were transferred to the laboratory. Larvae of the last instars are separated based on their host oak species and were reared till their entrance to pupa stage. The weigh of 4 day old female pupae was measured with a digital balance. Results showed neonate larvae of T. viridana in Mirabad and Pardanan enter oak buds after being hatched in 25^th Februray and 10^th March, respectively. Larvae enter 2'd instar after eating the internal contents of oak buds, then the third and 4^th instar larvae consume whole buds and even oak leaves and after development to the 5^th larval instar and roll the leaves and enter pupal stage in Mirabad and Pardanan regions. The occurrence of the peak of adult insects in Mirabad and Pardanan was recorded in 20^th May and 7^th June, respectively. Adult activities take two months. The pupa which is formed on Q. infectoria was the heaviest. Attacked trees from early May onwards revitalization and create a new leaf. New leaves, pale green and are smaller than normal leaves. Unfortunately, in this situation local people to imagine of wizened of damaged trees, they proceeded to cut them.