Experiments　for　single　phase　natural　circulation　flow　under　rolling　motion　were　performed　to　reveal　the　mechanism　of　the　variation　in　thermal　hydraulic　performance.　The　study　was　conducted　in　a　narrow　rectangular　channel,　at　pressure　of　0.2　to　0.3　MPa.　The　subcooling　temperature　ranged　from　50　to　90　K,　and　heat　flux　ranged　from　30　to　60　kW/m2.　With　temperature,　heating　power,　pressure　drop　and　mass　flux　measured,　the　flow　resistance　and　heat　transfer　characteristics　were　studied.　The　results　show　that,　with　the　increase　of　rolling　amplitude　and　frequency,　the　cycle-average　mass　flux　decreases,　and　cycle-average　friction　factor　increases.　The　heat　transfer　performance　is　more　complex　than　flow　resistance　under　rolling　motion　condition,　because　rolling　motion　can　not　only　disturb　the　thermal　boundary　layer　but　also　reduce　the　cycle-average　mass　flux,　the　former　enhances　heat　transfer,　while　the　later　results　in　heat　transfer　deterioration.　Rolling　motion　under　natural　circulation　condition　will　diminish　heat　transfer　in　entrance　region.　©　2016　Association　for　Computing　Machinery　Inc.　All　Rights　Reserved.