Expansible soils are those which will suffer considerable swelling and volume change when subjected to water. The resulting swelling pressure may cause complete destruction of such light structures as irrigation canal linings, floor slabs, etc. Based upon previous investigations, swelling of clayey soils has been blamed for failure of many irrigation canals in Iran and in other countries of the world. The main factor in these damages is the variation in moisture content which in turn would cause volume changes. In the present research, effects of cyclic wetting and drying on swelling potential of clayey soils has been investigated. For this purpose, three different clay samples were collected from three locations in south, northwest and central parts of Iran. The samples were tested for determination of their index properties, including grain size distribution, Atterberg Limits, specific gravity, and compaction. The swelling tests were conducted in odometer cells, where percent swelling was measured in five wetting and drying cycles. To investigate the effects of initial moisture content on swelling potential, the samples were tested at shrinkage limit, below shrinkage limit as well as above the shrinkage limit. Each sample was prepared to undergo five treatments of three replications. The results indicated no matter what the initial moisture content of the samples tested, the swelling potential was considerably reduced due to the imposed wetting and drying cycles. For some samples, reduction in swelling potential was observed in the second cycle, while for others it occurred in the third. Therefore it is concluded that one can control the negative aspects effects of the swelling soils. To perform the wetting and drying cycles before any canal lining would notably reduce the swelling potential and prevent the next probable forthcoming destructive effects of soil swellings.