The impact of introduced fungal pathogen Entomophaga maimaiga on population density of Lymantria dispar (L.) was studied in Bulgaria and Serbia during the period 2009-2014. In many localities, strong mortality was observed not only during the larval development but also in the pupal stage of the host. The average annual gypsy moth mortality caused by E. maimaiga in Bulgaria varied between 66.5% and 86.8%, and in Serbia – between 62.8% and 98.8%. The pupal mortality in Bulgaria and Serbia varied between 11.7-33.1% and 0.4-6.3%, respectively. The analysis of the biological material showed that the number of dead pupae was considerably high, in spite of the established small amount of the pathogen’s azigospores. The number of azigospores in L. dispar dead pupae in three studied localities in Serbia varies strongly (12-30 per а view field), but the average values are very close (2.33-2.90).