To insure optimal fruit yields of greenhouse tomatoes crop in Mansoura, Egypt, when greenhouse day temperatures can be in excess of 50 ºC, planting was dictated to be in late April to early September. To reduce daylight temperatures during summer months of 2007, fan-pad cooling system was examined under different glazing materials in a 32 m2 greenhouses: 1) corrugated fiberglass reinforced plastic (FRP), and, 2) double layer polyethylene sheets (PE). Tomato plants (Ebesia verity) were transplanted on 21 April, 2007 into 60 plastic pots in each greenhouse with plant density of 2.5 m². At transplanting the cooling system of 2.4 x 1.0 m in the west wall and one extracting fan in the east wall was automatically activated when the two greenhouses air temperatures reached to 28 ºC. Air temperature, relative humidity, wind speed, and total solar radiation entering the greenhouse were measured and recorded on a data-logger to analyses their correlation with tomatoes crop yield response. A mathematical model was developed to simulate microclimate on and around leaf surface for greenhouse tomatoes. The obtained results revealed that the air temperature and relative humidity inside the two greenhouses of 28.5 ºC and 29.8 ºC, 53.3% and 55.7%, respectively were maintained during summer months at and around noon. Furthermore, the obtained data revealed generally high uniformity of the microclimatic conditions within the greenhouse, in the lengthwise (east-west) and vertical directions. In contrast to that, there was a little variation across the width of the greenhouse (north-south) which arose as a result of solar radiation intensity and wind actions. It can be concluded that, due to the optimal level of microclimatic conditions inside the two greenhouses with an evaporative cooling system, they produced fresh yield of 8.796 and 7.356 kg/m2, respectively, consequently, greenhouse 1 increased the fresh yield by 19,58% as compared with the greenhouse 2. It must also be concluded that in order to obtain completely uniform microclimatic conditions throughout the volume of the greenhouse, it is desirable to install shading black net on the roof of greenhouse.