Quite often concrete strength parameters have to be determined at an early age. Due to the strong correlation existing between the mechanical and acoustic properties of concrete, ultrasonic devices can be used for this purpose. However, the ultrasonic pulse velocity (UPV) is affected by many factors, and it makes a great difference whether the concrete is subject to test at an earlier age or at a later time of exploitation. Since the elevated temperature of the environment promotes the shrinkage processes in hardening concrete, development of cracks and, therefore, a decrease of the UPV in concrete are to be expected. This paper describes the effect of non-isothermal high temperature (up to +30 °C) on the UPV in concrete. Influence of elevated temperature on the UPV in the concrete mass has been evaluated by determining the depth of the surface layer, at which the development of micro-cracks in the upper layers have no significant effect on the acoustic properties in concrete if an indirect transmission is applied for sounding.