The strain induced heavy hole and light hole exciton splitting of ZnSe 1-x S x (x<0.1) epilayers grown on misoriented GaAs (001) substrates has been studied by reflectance spectroscopy. The heavy hole and light hole exciton energies are determined by the composition of the layers. It was concluded that for both thin (largely unrelaxed strain) and thick epilayers (with largely relaxed strain) misorientation of the substrate results in increase of x, i.e., in increasing incorporation of sulphur. However, the additional strain expected due to the increasing incorporation of sulphur with misorientation was not observed due to partial strain relief of the epilayers grown on misoriented substrates. The optical quality of the epilayers is tilt angle dependent and is best for about 10° tilt from the (001) direction.