The influences of return bend on the two-phase flow patterns for air-water mixtures inside 6.9 and 3 mm smooth tubes are investigated in this study. For D=6.9 mm and at a mass flux of 50 kg/m2 s having a quality less than 0.1, no influence on the flow patterns is seen at a larger curvature ratio of 7.1. However, as the curvature ratio is reduced to 3, the flow pattern in the recovery region is temporarily turned from stratified flow into annular flow. But this phenomenon is suppressed again when the quality is increased to 0.3. The temporarily flow pattern transition phenomenon from stratified flow to annular flow is again suppressed when the tube diameter is reduced to 3 mm. It is likely that this phenomenon is related to the influence of surface tension and the reduction of developing length. Based on the present flow visualization, two flow pattern maps are proposed to describe the effect of return bend of the transition of two-phase flow pattern for 3 and 6.9 mm diameter tubes. An empirical fit of the observed length of the temporary annular flow in the recovery region is proposed that gives good predictions with the present data.