One of the most important factors in drug addiction is stress. It has been shown that animals with prenatal stress history are more risky for drug dependence. It have also been shown that frontal cortex play a role in drug dependence. In the present study the effects of two kinds of mild stress during pregnancy on the development of frontal cortex in Wistar rats (250-300 g) were investigated. Female rats (n = 8) were crossed with male rats and then were exposed to a random daily mild stress trial (5 min stress followed by five min rest in a 20 min period/day) until the 17th day of pregnancy. Two kinds of stress were applied, noise stress, by means of a tap on the animal cage with an iron tube and immobilization. On the day 17, the animals were anesthetized by diethyl ether and the embryos were taken out surgically. The embryos were fixed in formalin 10% for a week and then cross sectional procedure were performed. The sections were stained with H&E and evaluation was performed by motic program for the prefrontal cortex layers and laso cell counting. The results showed that thickness of the frontal cortex in the groups in which received stress was reduced. Cell counting also reveal that number of cells in the frontal cortex layers in experimental groups are lower than control one. In conclusion, present experiments showed that uncontrolled stress can change the structure and cytoarchitecture of frontal cortex which may be responsible for higher risk of drug abuse among the children of mothers with stress history during pregnancy.