A study was conducted to determine the temperature-humidity index (THI) and to assess the effect of evaporative cooling system (ECS) on the performance of gestating sows during summer season.  A total of 91 sows were used in the study, 49 sows were housed with ECS on the first 60 days of gestation (treatment 1) and 42 sows were housed in conventional housing system all throughout their gestation period (treatment 2).  The THI in treatment 1 and 2 ranges from 73.3`-76.49 and 75.23-79.28, respectively.  It was found that ECS does not have a significant effect on the gestation period, weaning weight, back fat thickness at farrowing, litter size born alive, litter size at weaning, total pigs born, and mortalities of sows.  However, it was found that ECS significantly affects the birth weight, back fat thickness at weaning, and weaning to estrous interval of sows.  Based on the 0.75 days significantly lower difference in the weaning to estrous intervals of sows from ECS, partial budget analysis revealed that 107,500.5 PhP house was added to the net profit of the farm due to the reduction in feeds costs.  Therefore, the use of evaporative cooling system to counter the negative effects of summer heat stress on the performance of the gestating sows was economically feasible in a commercial swine production enterprise.