Asian pear is a new horticultural crop in Iran, therefore, its management for higher yield and higher quality can play an important role in its economic production in appropriate growing areas. This study was carried out to determine a mathematical model between fruit diameter with volume and fresh weight and pomological evaluation of six cultivars of Asian pear including early (KS7, KS6), mid (KS11, KS13) and late (KS8, KS12) season. This study was carried out in research orchard of horticultural science department, Tarbiat Modares University, Tehran, Iran in 2008-2010. Fruits diameter, volume and fresh weight were measured by destructive and non destructive methods. Results of the relationship between diameter and volume and fruit fresh weight indicated that there was a strong correlation between fruits diameter with volume and fresh weight in all cultivars. There was no significant difference between measured fruits volume and fresh weight in comparison with estimated data based on fruit diameter which showed appropriate equations were finely fitted model to estimate the fresh weight and volume of fruit using fruit diameter. General equations from combined data of six cultivars showed that Y=-6.43+2.703X and Y=-6.31+2.68X were the best fitted models for estimating fruit volume and fresh weight based on fruit diameter, respectively. Evaluation of pomological traits showed that fruit loss (%) in late cultivars was high, thus their ultimate fruitset was low. Also there was significant difference in fruit yield between different cultivars. Therefore, KS13 with 6.01 kg tree-1 had the highest fruit yield and KS12 with 2.91 kg tree-1 had the lowest fruit yield.