Lens arrays of gradient-index (GRIN) rods that project an erected unit magnification image are used in light sources of LED printers. It is shown how alignment accuracy of the GRIN rod affects imaging performance to maintain the image uniformity. The coordinates and inclinations of the chief and marginal rays of the GRIN rod that has a different object distance or is tilted are analyzed with the ray matrix. We compare the ray coordinate shift with the object distance difference with that with the GRIN rod optical axis tilt. The image shift with the tilted GRIN rod is several times larger than that with the different object distance of the GRIN rod. However, the image by the tilted GRIN rod shifts parallel on the image plane without being almost blurred. Consequently, the GRIN rod tilt should be minimized sufficiently.