The fluid mixing in a curvilinear pipe flow of polymer solutions was investigated using the flow visualization. The number of curves N was set at 1, 6, 32 and 60. As a viscoelastic fluid, polyacrylamide (PAA) solutions of 0.05 and 0.1wt% were used. It was found that the drastic change of the secondary flow pattern strongly promoted the fluid mixing at N=60 for PAA solutions. The Reynolds number, at which the fluid mixing was promoted, became smaller with the increase in concetration of polymer solution.