An experimental study has been conducted to investigate the heat/mass transfer characteristics within film cooling holes of square and rectangular cross-section. The experiments for this study have been performed using a naphthalene sublimation method, and the flow field has been analyzed by numerical calculation using a commercial code (FLUENT). The rectangular cross-section has the aspect ratio of 2 and the same hydraulic diameter as the square cross-section. A duct flow enters into a film cooling hole in a cross-direction. For the film cooling hole with square cross-section, it is observed that the reattachment of separated flow and the vortices within the hole enhance considerably the heat/mass transfer around the hole entrance region. The heat/mass transfer on the leading edge side of hole exit region increases as the blowing rates decrease because the mainflow induces a secondary vortex. Heat/mass transfer patterns within the film cooling hole are changed slightly with the various Reynolds numbers. For the film cooling hole with rectangular cross-section, overall heat/mass transfer characteristics are similar with those for the square cross-section. However, heat/mass transfer on the leading edge side of hole entrance region has two peak regions due to split flow reattachment, and heat/mass transfer on the leading edge side of hole exit region is less sensitive to the blowing ratios than the square cross-section case.