The main objective of this study is to experimentally evaluate the effect of the air precooler heat transfer area on the effectiveness of a two-stage evaporative air cooler. To the best of our knowledge, this effect has not been studied before. In the experimental unit used, there were three identical heat exchangers to precool the ambient air prior to its flow into the direct evaporative cooling unit. These heat exchangers can work individually or be combined to control the total heat transfer area of the air precooler. In addition, the effectiveness of the two-stage system was measured as a function of the ratio between the mass flow rate of water flowing over the packing and the mass flow rate of the dry air passing through the packing; the effectiveness also depends on the mass flow rate of water flowing into the precoolers. The data obtained showed that there is an optimum value for the air precooler heat transfer area at which the thermal performance of the two-stage evaporative cooler has the maximum value. Moreover, the system effectiveness improved with the rate of flow of water into the first and the second precoolers. Note that the optimum value of the precooler heat transfer area should be determined accurately for each set of design and operating conditions.