Tomato (Solanum lycopersicum L.) is one of the most important vegetable plants in the world. It originated in western South America, and domestication is thought to have occurred in Central America. In order to study the effect of polyethylene sheet as mulch on water requirement and yield of tomato, an experiment was carried out as factorial layout based on a randomized complete block design with four replications in Fariman fields, during growing season 2011-2012 years. The first factor was with/without mulch application and the second factor was four irrigation intervals including 5, 7, 9 and 11 every days. Plant height, the number of flowers and fruits, yield, fruit weight and brix index of tomato were measured. The result showed that mulch and irrigation interval treatments were significant on reproductive characteristics such as flower number, fruit number and fruit weight of tomato, but they had not significant impact on plant height. That plant height and the number of flowers and fruit in mulch treatments were higher in comparison with without mulch. Mulch had not significant effect on fruit brix. The highest yield was obtained from 5 days irrigation which had not significant difference with seven days irrigation. At the first and the second sampling stages flower numbers with mulch application were higher than without mulch. It seems that mulch caused early rippenning, increasing in reproductive growth and yield of tomato. The fact that the irrigation could be delayed in two days using mulch would cause optimal use of water and the possibility of increasing cultivating area