InGaP epilayers were grown on the on-axis cut, 2 degrees off; 6 degrees off; and 10 degrees off GaAs substrates by organo-metallic vapor phase epitaxy, and the influences of crystallographic misorientation of the substrate on the structural proper-ties such as lattice mismatch, elastic strain, lattice curvature, misfit stress, X-ray line-width, and microhardness of the epilayers were investigated in this study. The material characterizations were carried out by the TXRD (triple-axis X-ray diffractometer) and the nanoindenter. With an increase of the substrate misorientation angle (S.M.A.), the relative incorporation of Ga atoms on the substrate surface was found to increase. Also, with an increase of S.M.A., the X-ray line-width of the InGaP epilayer was reduced, indicating that the crystal quality of the epilayer could be improved if the misoriented substrates were used. The elastic accommodation of the strain-free lattice misfit was found to be more remarkable in the misoriented samples. It was demonstrated, for the first time that the microhardness of the InGaP epilayer decreased with an increase of S.M.A. This indicated that the variation of microhardness of the epilayer was related to the improvement of the elastic characteristics and atomic displacement induced by the misoriented substrate. The results obtained demonstrated that the elastic characteristics and the crystal quality of the InGaP epilayer were remarkably enhanced and the microhardness of the epilayer decreased when the misoriented substrates were employed.