We have investigated asymmetric dislocation density and anisotropic lattice relaxation of ZnSe epitaxial layer grown on (001) GaAs substrate by MBE. Double-crystal X-ray rocking curves for (004) and {115} reflections were measured as a function of the azimuthal rotation angle of the sampel. For (004) reflection both the peak separation between the substrate and the epilayer and the FWHM of the epilayer peak vary sinusoidally as a funcion of the azimuthal angle. The results showed that the epilayer is tilted along [110] direction by 134" with respect to the substrate and also has a maximum value of FWHM along [110]. Fron {115} reflections it was found that the strain along [110] is smaller than that along [1-10], inducating that the layer suffered anisotropic lattice relaxation. The direction of larger relaxation is not consistent with that of the maximum FWHM corresponding to the high density of dislocations. The reuslt suggest that the asymmetry in dislcoation density is not responsible for the anisotropic relaxiation of the ZnSe epilayer.ayer.