We studied the effect of In segregation on the optical and structural properties of GaInNAs/GaAs quantum wells (QWs). The segregation model developed by Muraki etal [Appl. Phys. Lett. 61, 557 (1992)] is used to calculate the composition profiles of the QWs with different segregation efficiencies of In atoms. Confinement potentials of electron and hole are then derived, from which energies of electron and hole are numerically calculated by serving the Schrödinger equation. The effects of valence band mixing and strain are included in the calculations of the energies of electron and hole. The optical transition energy of the QWs is then obtained from the energy difference of electron and hole. It is found that the blueshift in transition energy due to segregation is mainly affected by strain rather than by composition in the studied QWs. Calculations using the segregation model together with the dynamical theory of x-ray diffractions are also carried out for the segregated QWs. The results indicate that the behavior of In segregation in Ga0.65In0.35N0.015As0.985/GaAs QW can be resolved by both photoluminescence and x-ray diffraction for the segregation coefficients larger than 0.7.