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 the earlier age or at a later time of exploitation. Since the UPV in ice is higher than in water, an increase of the UPV in concrete are to be expected. This paper describes the effect of frost on the UPV in concrete. The studies were carried out with short-term and long-term freezing of concrete specimens at active phases of the hydration. Significant changes in the UPV in concrete, caused by the interaction of frost and moisture, have been established.