Unconfined compressive strength (Su) is one of the soil engineering parameters used in geotechnical designs. Due to the temperature changes caused by some human activities, it is important to study the changes in Su at different temperatures. For this purpose, kaolin, illite and montmorillonite clays with a liquid limit (LL) of 47, 80 and 119 respectively, were tested in a temperature-controlled cell in temperature range of 20 to 60 ℃. The results showed that the pore water pressure is a function of temperature and by heating, pore water pressure in the samples increased. In all three types of clay, the Su decreased linearly with increasing temperature. The reduction of Su in kaolin is more than illite and in illite is more than montmorillonite. The reason for this reduction, might be due the difference in the mineralogy of the clays. The results of unconfined compressive tests at different temperatures were simulated using hypoplastic model.