In this study, the phase angle of the first normal stress difference in oscillatory shear flow has been investigated from both experiments and simulations. Nonlinear constitutive equations and materials were selected to minimize the higher harmonic contributions in the stress signal. The upper convected Maxwell model and the Oldroyd-B model were selected, and several complex fluids including Boger fluids, highly viscous polymer solution and highly elastic polymer gel were selected for that purpose. The phase angle (${delta}_2$) of the first normal stress difference was found to be in the range from $90^{circ}$ to $-90^{circ}$, as was confirmed from both constitutive equations and experiments. Two models showed similar response in the phase angle of the first normal stress difference but different response in the phase angle of the shear stress. It was also found that the phase angle of the first normal stress difference is governed only by the Deborah number of the material within the material range we have covered in this study.