It is important to know the triboelectric charging characteristics of a toner to control the mono-component magnetic toner development system. In this paper, we studied the relationship between the triboelectric charge to mass ratio (Q/M) of a mono-component magnetic toner and several parameters of magnetite incorporated in the toner. In order to remove the influence of different magnetic force on magnetic toner charging behavior, we measured the triboelectric charge of the mono-component magnetic toner against an iron oxide powder carrier. The concentration of magnetite in the toner was changed from approximately 5 to 55 wt%. We used several kinds of magnetite differing in their particles size and shape. We found that the Q/M decreased proportionally with an increase in magnetite concentration. We assumed this Q/M decrease was related to the magnetite on a toner surface. We calculated the number of magnetite particle on a toner surface, and total cross-sectional area of magnetite particle on a toner surface. The result suggests that total crosssectional area of magnetite on a toner surface has no effective triboelectric charge. In conclusion, we can describe a relational expression between Q and the parameters of the magnetite as Q=Q0×(1-Sm/S), where, Q is toner charge, Q0 is charge for the magnetite-free toner, S is surface area of a toner, and Sm is the total crosssectional area of magnetite on a toner surface.