The turbulent friction drag of Newtonian fluid flow can be reduced dramatically by adding small amount of polymers or surfactants. Such drag-reducing (DR) effect of these non-Newtonian solutions has been utilized in some practical applications such as oil pipeline, district heating and cooling systems, etc. While the DR effect has been studied well in simple wall turbulence, such as turbulent plane channel and straight pipe flows, few studies have focused on the flows of these non-Newtonian solutions in more complex geometries where the mean flow is three dimensional and massive separations and/or significant secondary motions take place. In the present study, we experimentally investigate a surfactant-solution pipe flow over a semicircular orifice. A 500 ppm solution of a commercial drag-reducing additive (LSP-01M) was used as the working fluid, and we at first confirmed the DR effect of this solution in a turbulent straight pipe flow. Then, the flow in a pipe with a semicircular orifice was investigated based on stereoscopic PIV measurements. The focus is particularly placed on how the secondary flow patterns and turbulence intensities downstream the orifice is affected by the addition of surfactant in comparison with the Newtonian fluid (water) case.