The transfer drum (TD) technology is one of the toner transfer processes used in laser printers. In this process, the paper is clamped and attracted to the TD. An electrical attraction occurs between the paper and the TD when a transfer voltage is applied to the TD in opposite polarity to that of the toner charge. A sufficient charge density is accumulated on the paper surface and an electric field is created between the paper and toner particles. As a result, the charged toner is electrostatically transferred from the photoconductor (PC) to the paper. Since the effect of the transfer voltage across the paper causes the electrostatic transfer, it would be important to understand the transfer phenomena in detail by studying transfer efficiency under different conditions.The experiments for this study were carried out in a real printing process by applying different transfer voltages to some commercial paper grades under given humidity levels. The transfer current and toner amounts were measured to characterize the transfer situation. The transfer efficiency was examined as a function of transfer voltage. The experimental results show that the amount of toner transferred to the paper and the transfer current for a certain paper grade under certain humidity conditions are directly related to each other and functions of the transfer voltage. Overall, the relative humidity (RH%) is a very important variable even within fairly narrow ranges. In addition, the results show that the transfer efficiency expressed by the toner amount is in quantitative agreement with the ideal transfer profile presented by Tombs.