Abstract: This study was carried out to investigate virulence gene(s) frequency of wheat stripe rust (Puccinia striiformis f. sp. tritici) populations during natural epidemics, in nine different fields, located in the regions of Southern Aegean and Western Mediterranean. Stripe rust uredospores were collected from diseased plants in 2000 and 2001. Virulence of pathogens were determined by seedling test. The results showed that virulence gene frequency on rust population varies depending on the type of genes. The genes which have high virulence frequency were more stable. In both experimental years, it was established that the virulence frequency of Yr1, Yr2, Yr3a, Yr9, Yr17, Sd and So genes ranged between 7.8 and 100% in all populations while Yr6, Yr7, Yr8 and Yr10 genes were observed in all locations.