In the lithographic processes of VLSI's, high setting accuracies between masks and wafer are required. The methods using moiré signals obtained by gratings were found to give very high alignment accuracies. In this paper, influences of the inclination of gratings for the alignment accuracies in modified and differential moiré systems have been investigated. The moiré signals and the alignment point have been calculated using computer simulation. As a result, it has been shown that the effects are small and the inclinations do not affect alignment accuracies in the moiré alignment systems.