Abstract: Local void fraction of air-water bubbly flow in an inclined circular tube（ID 50mm） was obtained by optical fiber probe method.The results show that the averaged void fraction decreases with the increasing of the inclined angle,whereas its trend is moderated when the inclined angle larger than 5 degree.The void fraction nearly does not change with radius except in the near wall region where it has a peak value and falls to the minimal value in vertical condition and the typical saddle pattern profile is observed.Under inclined condition,bubbles move to the upper wall and congregate,therefore,the wall peak in the upper near wall region is enhanced nevertheless is weakened in the lower near wall region,even disappears with a larger inclined angle.