Studies were carried out to find out the efficacy of Egyptian strain (BA1) and exotic European strain (Hb1-3) of entomopathogenic nematode; Heterorhabditis bacteriophora against full-grown larva of Galleria mellonella L. Infection took place in plastic cups (100 cc) half-filled with moistened sterilized sandy soil that treated with 5 concentrations of each of the two strains of nematode; 5, 10, 20, 40 and 80 infective juveniles (IJs)/cup. Two densities of Galleria (1 and 5 larvae/cup) were used for each strain at each concentration. It was found that the efficacy of entomopathogenic nematode strains, on the full-grown larvae of G. mellonella was concentration dependent; i.e. the mortality percentage increased as the IJs concentrations were increased. Individual treatment (one larva/cup) led to more efficacy than using 5/cup at 25°C. The production of infective juveniles from G. mellonella larvae infected at concentrations of 1, 2, 4, 8 and 16 IJs/cup was, generally, higher in BA1 strain compared to Hb1-3 strain. The histopathological observations revealed variable effects on G. mellonellalarvae after infection with the entomopathogenic nematode. Muscles suffered destruction in the fibrillate with some fragments and fat body tissues showed high vacuolation.