Water is one of the most important resources in human societies. Regarding many uses of water in agriculture and its low efficiency, it is essential to find out practical approaches in improving irrigation methods and optimizing use of water in order to reduce the adverse effects of drought in agriculture. One of these methods is deficit irrigation. Water condition affects pest population directly and/or indirectly by changing host suitability for insect pests and altering host resistance. In order to study the singular effect of water stress and together with pest stress on corn yield, an experiment was conducted in the research farm of Isfahan University of Technology. In two separate parts of the field, sprayed and not sprayed, a factorial design, based on the completely randomized blocks, was carried out with three treatments of irrigation regimes including intensive stress (50%water requirement), moderate stress (75% water requirement) and no water stress (100% water requirement) in four stages of corn growth, first stage (from seed germination until tasseling), second stage (from tasseling until milky), third stage (from milky until harvest) and the whole period of corn growth, in four replications for one year (2005). Pest populations were evaluated using sweeping nets (6 strokes) and with removing three corn plants from each plot. Water requirement of corn was determined by Penman - Mantheith equation and Cropwat software. Water stress was applied through constant irrigation period and variable irrigation regimes in all growth stages. Results showed that applying water stress on corn reduced yield and other agronomic characters. Reduction yield under moderate stress was 50% and under intensive stress was 60% in sprayed part of the field. This reduction in not sprayed part was 65% under moderate stress and 68% under intensive stress. The effect of moderate stress was not significantly different from no water stress treatments on agronomic characters. In sprayed condition, particularly, applying moderate stress in first stages of corn until the first of third stage is suggested in drought condition. Applying water stress on corn in all sampling weeks of pests had significant effect (P?0.01). Water stress increased Thrips tabaci and Tetranychus urticae populations. The highest mean number of T.tabaci and T . urticae were observed in intensive stress during the whole period of corn growth. The lowest mean number of T.tabaci and T . urticae were observed in no water stress treatments. On contrast applying water stress reduced Empoasca decipiens and Psammotettix alienus populations. The highest mean number of E.decipiens and P. alienus was observed in no water stress treatments.