Abstract: Experimental studies of single-phase natural circulation flow and heat transfer under a rolling motion condition are performed. Experiments with and without rolling motions are conducted,and the effects of rolling motion on natural circulation heat transfer are obtained. The experimental results show that the flow fluctuation caused by rolling motion enhances the heat transfer,and the heat transfer coefficient of natural circulation flow increases with the rolling amplitude and frequency. Analysis of data shows that the effect of heat capacity of heated tube can not be neglected and Reynolds number of acceleration is introduced to employ the effect of heat capacity. Based on the experimental data,an empirical equation for the heat transfer coefficient under rolling motion is achieved. The calculated results agree well with experimental data.