Study on relationship between infestation of two spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) and yield loss in tomato, Lycopersicon esculentum Mill. revealed that one mite released to a tomato plant 6 weeks after planting and allowed to feed for 3, 6, 9 and 12 weeks, reduced the final yield by 0.233, 0.689, 1.291 and 1.624 g per plant, respectively. Under similar conditions with same treatments a mite day reduced 16.4, 1.80, 0.96 and 1.18 mg of the final yield, respectively. Middle stage of the crop was the most critical period and mite infestation initiated at this stage can contribute to more than 50% of total yield loss due to leaf defoliation and reduction of chlorophyll content of the leaves. Economic injury levels (EILs) for tomato has been calculated based on the number of mites initially released and mite days during different growth stages. Though calculations based on these two parameters yielded similar information, for predictive purpose, the number of mites is more useful in quick decision making. This study was able to provide quantifiable decision making tools, by which the EILs can be fixed to enable the farmers to time their by application of acaricides.