The present study has been conducted to investigate the effects of Reynolds number on heat/mass transfer and pressure drop characteristics in a rotating smooth two-pass duct. For stationary cases, the heat/mass transfer and pressure drop Is decreased on turning region of both leading and trailing surfaces as Reynolds number increases. For rotating cases, increment of Reynolds number affects differently the heat/mass transfer and pressure drop on the leading and trailing surfaces. In the first pass, for example, the heat/mass transfer on the leading surface is greatly increased, though the heat/mass transfer on the trailing surface is almost the same. The reason is that effect of the main flow is more dominant than effect of secondary flow. In particular, it gave decrement of the heat/mass transfer and the pressure drop at turning region and upstream region of second pass for both non-rotating and rotating cases.