The purpose of this study was to investigate the optimal anti-scatter grid (grid) selection for digital radiography with a computed radiography (CR) system. Anterior-posterior lumbar spine radiographies were performed with no grid and grid ratios of 5, 8, 10, 12 and 14 under the same exposure conditions. An x-ray tube voltage of 80 kV and 20 mAs were used in all radiographies. Signal-to-noise-ratio (SNR) for all radiographic technique was measured as an image quality index. To consider the effect of image quality, scatter fractions, incident doses to imaging plate (IP) were also measured. The use of grid ratios of 10, 12 and 14 provided higher SNR than those of the images with grid ratios of 5 and 8 when same exposure conditions were used. Phantom radiographs also indicated that the images with 10, 12 and 14 grid ratios improved image quality over that obtainable with images of lower grid ratios although the images look noisy.