The tomato fruitworm (Helicoverpa armigera) is one of the key pests in Iran, attacking to a wide range of important crops and causes serious damage. Worldwide reports indicated that this pest have developed resistance to many insecticides, and lead to the reduced efficacy. As monitoring and early detection of the insecticide resistance in one of the accepted principles of integrated pest management, in this research, we studied the resistance status of the tomato fruitworm populations from Alborz province (Karaj, Nazarabad, Hashtgerd) against indoxacarb, thiodicarb, deltamethrin and chlorpyrifos. First, the populations were collected from the farms, then the laboratory cultures were established and bioassay were done using the IRAC protocol. Topical application of insecticides was used as bioassay method for deltamethrin and chlorpyrifos and diet incorporation method for indoxacarb and thiodicarb on third-instar larvae. The results indicated that Nazarabad population has developed resistance against thiodicarb) resistance factor =RF= 12.63), while Karaj population showed resistance to deltamethrin (RF=14.68). To prevent increased resistance in future, it is recommended that farmers use these two compounds as less as possible, instead use alternative compounds with different mode of action. Moreover, resistance against indoxicarb and Chlorpyrifos were not seen, as the RFs were calculated below 10. The results of this research, can be used in optimized and correct use of insecticides against this pest.