This paper presents the analysis of the influence of temperature on mechanic properties of the base material and welded joints made of high strength steel. The joints were welded on S690QL high strength steel plates using the Metal Active Gas (MAG) Welding and two filler materials of different properties. Since the steel S690QL belongs to a group of steels with high strength, the aim of this paper is to determine the temperature at which strength starts to decrease. Experimental tensile testings of the welded joints were performed at five different temperatures in the range from 20 to 550 °C.