In process of reinforced concrete (RC) box structure, the heat of hydration may cause serious thermal cracking. This paper reports results of hydration heat control in mass concrete using the oscillating heat pipe. There were three RC box molds ($1.2m{ imes}1.8m{ imes}2.4m$) which were different from each other. One was not equipped with pulsating heat pipe. The others were equipped with pulsating heat pipe. All of them were cooled with natural air convection. The pulsating heat pipe was composed of 10 turns of serpentine type copper pipe whose outer and inner diameters were 4 and 2.8 mm respectively. The working fluid was R-22 and charging ratio was 40% by volume. The temperature of the concrete core was approximately $55^{circ}C$ in the winter without pulsating heat pipe. For a concrete with pulsating heat pipe, however, the temperature difference with the outdoor one reduced up to $12^{circ}C$. The index figure of crack was varied from 0.75 to 1.38.