Abstract: This study was conducted to evaluate the virulence of 10 Iranian isolates of entomopathogenic fungi, Beauveria bassiana (Bals.) Vuill. and Metarhizium anisopliae (Metch) Sorok. and introduce the most virulent isolate for microbial control of the house fly Musca domestica L. under the laboratory conditions. Three bioassay methods were used: Topical, oral and bait method. Fungal isolates were first screened by immersing adults and medium sized larvae in a suspension containing 108 conidia mL-1. Percentage mortalities ranged from 28-100% were recorded for adults and larvae and five isolates were found to be relatively more virulent. Data clearly show that there is a wide range in the response of the two stages (larvae and adult) of the house fly to the action of the tested isolated of B. bassiana and M. anisopliae. LC50 values in bait method for adults were 1.65x106, 1.7x106, 1.9x106, 2.9x106 and 3x106 conidia g-1 for the 5 highly virulent isolates designated Ma437C, Bb187C, Bb429C, Bb428C and Bb796C, respectively. Dose of 5x107 conidia g-1 bait resulted in up to 90% mortality within 3.5-6.5 day after exposure. Topical application for larvae resulted in LC50 values of 7.3x104, 1.1x106, 1.6x106, 2x106 and 2.9x106 conidia mL-1 for the isolates, respectively. Oral application of 109 conidia g-1 larval bedding resulted in larval mortalities of 98.4, 5 6 and 35.2% for Ma437C, Bb187C and Bb429C, respectively. Due to lower LC50 and LC90 values and shorter lethal time, Ma 437C was the most virulent isolate for house fly larvae and adult.