The fully developed Oldroyd-B fluid flow through rotating square ducts was numerically studied. The effects of the rotation on secondary flow, axial velocity, and axial normal stress were examined in detail. The results indicated that all of the secondary flow, the axial flow, and the axial normal stress were evidently affected by the rotation. The Taylor–Proudman phenomenon could be observed in the flow. For the secondary flow, the four vortices structure and the six vortices structure were described. Recent studies also showed the effects of rotation on the axial normal stress. The fully developed Oldroyd-B fluid flow through rotating square ducts was numerically studied. The effects of the rotation on secondary flow, axial velocity, and axial normal stress were examined in detail. The results indicated that all of the secondary flow, the axial flow , and the axial normal stress were evidently affected by the rotation. The Taylor-Proudman could could be observed in the flow. For the secondary flow, the four vortices structure and the six vortices structure were described. on the axial normal stress.