Abstract: Entomophaga maimaiga was isolated and described as the natural enemy of the gypsy moth in Japan, some parts of China and the Russian Far East, where it causes the periodical epizootics. It is not native entomopathogenic fungus in Europe. It was introduced for the first time in Bulgaria, in 1999. Recent data suggest that E. maimaiga is getting spread in Europe. Since the presence of E. maimaiga, in Central Serbia had already been determined, at 97 selected plots situated in: Belgrade, Valjevo, Krusevac, Kraljevo, Vrnjacka Banja, Blace, Prokuplje, Kursumlija and Negotin regions. In spring and autumn of 2012 and 2013 the assisted spread of E. maimaiga was perfomed, through the introduction of the infectious inoculum in the oak forests. E. maimaiga was dealt with fungus, which is particularly susceptible to the weather and the global warming conditions and the great drought, a special preparation of inoculum was made. In the following year the mass epizootic of the gypsy moth caterpillars occurred, which implies that E. maimaiga caused the decline of the gypsy moth population. The detailed microscope survey showed the presence of numerous conidiospores and azygospores of the E. maimaiga in 83.8% of collected cadavers.