Magnetic powder dispersed carrier (MC) is studied in order to extend the life of developer, while achieving the fast charging rate for both positive and negative toners. This paper reports the influence of MC composition on the charging characteristics by clarifying the charging mechanism. The charging property of MC varies depending on which of the resins or magnetic materials becomes a doner or an acceptor of electrons. The polarity and the charging level of MC are evaluated by measuring the electronegativity of metal oxide in magnetic powder and the chemical property of functional group in resin. The charging rate of MC developer is faster by increasing the fraction of magnetic material in MC. It is found that MC attains fast charging rate without a charge control agent, (CCA) although the charging rate of conventional coated carrier is very low without AAC. Furthermore, the charge of MC does not decrease linearly with the carrier spent volume. The charge gradually increases for 200-300K prints from the start and then slowly decreases to the initial charge volume for 300-800K prints. Therefore, the life of the developer is the same as the machine life and no maintenance of the developer is required. The peculiar behavior of MC is due to the surface which possesses both electron donor site (magnetic particles) and acceptor sites (resin). The charge of toners mixed with MC, which are pre-stirred before the mixing, is larger than that without the pre-stirring. This phenomenon of MC can be explained by the mechanism that the charge arises not only by the difference in work function between toner and carrier but also by donation of electron from toner to positive site generated by pre-stirring of carriers. This charging mechanism enables the MC developer to be in a good toner charge condition during the printing with a fast charging rate in MC developer.