Abstract: Natural circulation characteristics in symmetrical loops under rolling condition were investigated theoretically and experimentally. Rolling experiments with a zero power load show that angular acceleration causes the fluctuation in branch flow channels, but has no influence on the middle channel. Full power experiments under rolling condition exhibited observable flow rate and temperature oscillations in each branch of the flow channel. The fluid oscillations in the side flow channels had the same period and phase with the rolling angle, while the fluid in the middle channel oscillates with half the rolling period.