Three entomopathogenic nematode strains, namely FIN, SAR and Hbs1 belonging to Heterorhabditis bacteriophora were selected and tested for pathogencity against newly moulted 6^th instar larvae of Agrotis ipsilon (Hufn.). All strains were pathogenic to the mentioned instar. Analysis of data revealed that the nematode strains, exposure period (24, 48 and 72 hours) dose (10, 20, 40, 70 and 100 of infective juveniles/larva) in laboratory experiments, (150, 300, 500, 700 and  900 of infective juveniles/larva) in field trial and application method (surface and subsurface of the soil) were significantly (P<0.05) affected larval mortality. It was found that the mortality rates were directly correlated with the applied doses, exposure period and different strains. Under controlled laboratory conditions the LC₅₀ values of treated 6^th instar larvae were 17.1, 30.9 and 41.1 infective juveniles (IJs) per insect for Fin, SAR and Hbs1 strains, respectively after 72h post-infection. Fin strain was the most virulent causing the maximum mortality; An inoculum level of 100 IJs/larva caused 98%, 80 and 72% after 72h post infection for Fin, SAR and Hbs1, respectively in laboratory. Under field conditions 93.3%, 73.3% and 63.3% mortality results were achieved at the subsurface application of nematodes versus 86.6%, 63.3% and 56.6% at the soil surface application with FIN, SAR and Hbs1 nematode strains respectively at the highest concentration (900 IJS/Larva), after 72h from infection. The LC₅₀ values of treated 6^th instar larvae were 6.0x10², 3.9 x10² and 6.2 x 10² at the subsurface of nematode application against 3.3 x 10², 5.2 x 10^2­­ and 6.9 x 10² at the soil surface of nematode application with Fin, SAR and Hbs1 nematode strains, respectively, 72h  post-infection. It is clear that the newly moulted 6^th instar larvae of A. ipsilon were more susceptible to Fin and SAR strains than Hbs1 when treated at the subsurface of the soil and the soil surface, respectively.