It is important to have better calibration method for the submicron dimension system as the semiconductor technology requires more accuracy on the metrology system. Gratings have been used as a standard reference for the magnification, and the precision laser diffractometer has been developed for the calibration of the grating pitch. The accuracy of the measurement may depend on the laser wavelength, the goniometer, and how to determine diffraction angles. As the accuracy of conventional diffractometry has been limited by the low resolution of diffraction angle and its determination, the rotary arm is extended and reliable high-resolution goniometer is opted, while a focusing lens is inserted between the grating sample and the detection plane to prevent the error due to the parallel shift of the diffracted beam, which might occur when the rotational axis of the arm does not coincide with the grating plane. Obtained values for all grating samples showed quite good repeatability, which is order of angstrom at worst. Incidence angle dependent fluctuation of measured value is shown to be quite small as expected. The grating pitch, certified as 288 nm by the manufacturer, is measured as 287.595 with a standard deviation ((sigma) ) of 0.017 nm at worst. The other grating, certified as 700 nm, is measured as 700.782 with a standard deviation of 0.054 nm at worst. The expanded uncertainty with the coverage factor of 2 is estimated to be 0.038 nm and 0.10 nm respectively.