Abstract: Rolling motion, as a typical ocean condition, has an important influence on the two-phase flow resistance in rectangular channels. Frictional characteristics of air-water bubbly flow in vertical narrow rectangular channel were investigated under rolling motion and atmospheric conditions, hoping to clarify the effect of rolling motion on two-phase flow. The test-section had a cross section of 40 mm×10 mm and the rolling periods and angles were 8, 12, 16 s, and 10°, 15°, 30°, respectively. The experimental results show that the frictional pressure drop fluctuates periodically with the rolling period. The fluctuation amplitude of frictional pressure drop increases with the decrease of rolling period and the increase of rolling angle，and increase of the average quality would result in the increase of the fluctuation amplitude.