In the present research, the viscoelastic fluid flow through 90-degree bend ducts was investigated both experimentally and numerically. The flow through 90-degree bend ducts has various industrial applications such as petroleum industry, pharmacy, food industry, and microfluidics devices. The particle image velocimetry (PIV) method was utilized to visualize the formation of secondary flows inside the curved channel. Also, numerical simulations were conducted using finite volume method. In order to couple velocities and pressure fields, the PISO algorithm was used. In the present research, the effects of various Reynolds numbers and curvature ratios on the secondary flow patterns inside the 90-degree bend ducts were studied. Furthermore, the effect of these two parameters on the first and second normal stress differences was investigated. The considered curvature ratios for curved ducts were equal to 0.05, 0.066, 0.1, and 0.2 at Re=10, 20, 30, 40, 50, and 100. The results showed that eight elastic vortexes were formed in the fully-developed viscoelastic flow though a straight channel. When the viscoelastic fluid enters the curved part of channel, these eight elastic vortexes interfere with the Dean vortexes and eventually two Dean cells are formed. The presence of first and second normal stress differences in viscoelastic flows resulted in stretching the Dean vortexes. In addition, the comparison between Newtonian and viscoelastic secondary flows through curved ducts showed that the strength of secondary flows in viscoelastic flows at the considered Reynolds numbers and curvature ratios was greater than Newtonian ones. Also, according to the secondary flow patterns in viscoelastic flow, the results of numerical simulations showed the possibility of postponing the Dean instability in viscoelastic fluids. Furthermore, the numerical results demonstrated that the first and second normal stress differences were constantly increased though the curved part of channel which led to stretching the Dean vortexes toward duct walls. Keywords: Secondary flows, Viscoelastic fluid, PIV, First normal stress difference, Second normal stress difference