The economic injury level of maize stem borer,Chilo partellus(Swinhoe) was determined for two maize varieties, Basi Local (susceptible) and CM‐500 (resistant). One‐day‐old first instar stem borer larvae, in varying densities, were released on 12‐, 17‐, 22‐ and 27‐day‐old plants. Irrespective of larval density, the maximum yield loss was encountered when plants were 12 days old. The yield loss gradually decreased in CM‐500 as well as in Basi Local as the crop grew older, though it was more steep in. CM‐500. A positive relationship was observed between larval density and yield loss in 12‐ and 17‐day‐old crop. With 22‐ and 27‐day‐old plants maximum yield loss was caused by 20 larvae/plant, instead of 24 larvae/plant. The economic injury level (EIL) was found to increase as the crop stage increased. In case of Basi Local. EIL was 1.24, 1.38, 2.56 and 3.36 larvae/plant for 12‐, 17‐, 22‐and 27‐day‐old crop. On the other hand CM‐500 required 1.16, 1.17, 8.86 and 14.13 larvae/plant for 12‐, 17‐, 22‐ and 27‐day‐old crop. A significant difference in yield loss in Basi Local and CM‐500 was found when 20 larvae/plant were released on 22‐day‐old crop.