The goal of this study is to measure the effect of daylight saving time on electricity consumption in the four provinces of Tehran, Yazd, Esfahan and Fars. A system of 24 equations, one for each hour of the day is estimated using the SUR method.The equations are estimated for the years 1382 to 1384 during which daylight saving time was in force. Then the model is solved for the years 1385 and 1386 during which daylight saving time was not in use. Comparing the results of simulated electricity consumption with actual electricity consumption, the potential amount of saved electricity is estimated. The results show that use of daylight saving time in the four provinces mentioned above, could have reduced electricity consumption by respectively 1,259,227 MW (equal to 3.2% of total electricity use) in 1385 and 1,555,273 MW (equal to 3.7% of total electricity use) in 1386. The monetary value of potential savings equals to 192,384,736,665 Iranian Rials in 1385 and 237,614,546,427 rials in 1386. In addition, use of daylight saving time can cause a reduction in the mean peak electricity consumption of the four provinces.