The sunn pest, Eurygaster integriceps Puton (Hemiptera: Scutelleridae), is the most important insect pest of wheat and barley. The population management of this pest is of major concern to wheat producers. One of the potential control strategies is to use entomopathogenic fungi. This study evaluates the pathogenicity of the fungus Metarhizium anisopliae var. major (Metchnikoff) Sorokin (Hypocreales: Clavicipitaceae) on the sunn pest, E. integriceps. Five concentrations of the fungus were utilized, ranging from 1×10⁴ to 1×10⁸ conidia/mL, accompanied by controls. Fifth instar nymphs and adults (a migratory summer population and a diapausing population) previously exposed to fungi were sown to isolate the fungi, and the growth parameters were analyzed. A direct spray technique was used to expose the isolates to the E. integriceps. The experiment was repeated four times, and mortalities of the insects for all treatments were recorded daily. The results showed that the mortality of infected nymphs was significantly higher than the mortality of control nymphs. Also, the longevity of infected adults was lower than the controls. The results also showed that diapausing adults of the sunn pest were much more susceptible to infection than the summer adults. Estimated LC₅₀ values for the M₁₄ isolate were 1.4 × 10⁶, 1.4 ×10 ⁵ , and 2.3 × 10³ spores/mL against the aestivation population, the diapausing population, and 5^th instar nymphs, respectively. Estimated LT₅₀ values using 10⁸ spores/mL of the Mm isolate on the aestivation and diapausing populations were 11.9 and 5.11 days, respectively. The results demonstrated that M. anisoplaie was effective on all of stages of E. integriceps. In addition, the nymphal stage was more susceptible than the adults.