Abstract In this paper by using modified scalar effective index method, first effective refractive index of straight and bent photonic crystal fibers are determined and then propagation parameters, such as chromatic dispersions for different structural designs of PCF, are obtained. By changing the values of affecting parameters in the bent PCF, such as different bent radius, distance between air holes Λ $\Lambda $ and air-filling factor d / Λ , $d/\Lambda ,$ the chromatic dispersion is determined in terms of propagating wavelengths. The obtained results of bent PCF are compared with the results of straight PCF. The results of the present paper might be useful in designing optical devices and sensing systems.