The present invention provides a one-component magnetic toner for developing an electrostatic charge image, which do not cause an image defect by toner aggregation or fusion even though a device is miniaturized and the processing speed of the device is accelerated, and which allows easy recycling of a toner cartridge. The one-component magnetic toner for developing an electrostatic charge image of the present invention is one comprising: toner particles comprising fine magnetic particles (A) and a binder resin; and fine magnetic particles (B) externally added to the toner particles, in which the maximum permeability (.mu.m.sub.A) of the fine magnetic particles (A) contained in the toner particles and the maximum permeability (.mu.m.sub.B) of the fine magnetic particles (B) externally added to the toner particles satisfy a relationship represented by the following formula (1) .mu.m.sub.B/.mu.m.sub.A.ltoreq.1.8 . (1)