A sleeveless magnet roller developing system was studied by using a non-magnetic toner and an iron carrier. A developing roller made from a sintered ferrite magnet, with 32 magnetic poles and 0.025 T in magnetic flux density, was employed in this study. Imaging characteristics and developing behavior were examined in the sleeveless magnet roller developing system in both normal and opposite developing directions. The influence of toner concentration on the developing characteristics was also examined. It was confirmed that the developing system had an optimum developing condition for best imaging properties. It was also found that the toner concentration in the developer was stable during continuous printing. These results suggest that developing characteristics can be controlled by automatic control of the toner concentration.