The present research was conducted to determine the percent self-incompatibility in some Asian pear (Pyrus serotina Rehd.) as well in European pear (Pyrus communis L.) cultivars. The experiment was carried out during 2006 and 2007 growing seasons. Pollen grains were collected and tested for viability using in-vitro pollen culture. For microscopic examination of pollen tube growth in the style, pollinated flowers were sampled and fixed in the FAA solution after 48, 72, 96 and 120 hour post pollination. At the time of flowering stage and during both seasons, Asian and European pear cultivars exhibited a reasonable overlap of flowering. Pollen viability test on Asian pear (as well as microscopic examination of pollen tube growth) in all the studied cultivars showed 55 to 70% pollen germination, indicating that pollen grains involved in the experiment were healthy and viable, although in most of the studied cultivars pollen tube stopped growth at a one third point to style ending. Results as based on the final fruit set (in-vivo test) showed a fruit set of less than 5% for Asian, European and as well for the native studied cultivars. So, one can conclude that all the studied cultivars were self-incompatible. Therefore, as for the future breeding programs, cross pollination is suggested within Asian pears as well as among Asian and European pears to create and produce working material of enough variability. In addition, in order to produce higher yields, it is necessary to carry out control pollination experiments (utilizing various cultivars as pollen and seed parents) to determine cross-compatible groups for the newly established Asian pear orchards in Iran.