Concrete protects the steel inside against several effects of the external environment. One of the most important of these effects is high temperature. Cover plays a critical role in concrete's protection on reinforcement against high temperature. In this study, the changes after high temperatures in mechanical properties of the reinforcement steels placed between 3 and 5 cm covers inside the mortar specimen prepared with CEM I 42.5 R and CEM II/B-M (P-L) 32.5 R cements were investigated. In order to ensure 3 and 5 cm covers 76 x 76 x 310 and 116 x 116 x 350 mm sized reinforced mortar specimen were prepared. These reinforced mortar specimens were exposed to 20, 100, 200, 300, 500 and 800 degrees C temperatures and after that on the steels taken out of these mortar specimen tensile strength, tests were applied in order to determine the mechanical properties. With the tensile strength tests performed stress-strain curves of the steel bars exposed to several temperatures were drawn. Besides, the yield and ultimate strengths of the steel bars were determined. The results of the study have shown that the larger the covers, the better the steel bars are protected against high temperatures. Copyright (C) 2010 John Wiley & Sons, Ltd.