A magnetic toner for developing electrostatic images, comprising at least a binder resin and a magnetic powder; the binder resin having 10 to 70 wt. % of a THF (tetrahydrofuran)-insoluble and a THF-soluble, the THF-soluble providing a molecular weight distribution in the chromatogram of GPC (gel permeation chromatography) thereof such that it provides a rate (Mw/Mn) of weight-average molecular weight (Mw)/number-average molecular weight (Mn).gtoreq.5, there are a peak in the molecular weight range of 2,000 to 10,000 and a peak or shoulder in the molecular weight range of 15,000 to 100,000 and a component having a molecular weight of 10,000 or smaller is contained in an amount of 10-50 wt. % based on the binder resin; the magnetic powder comprising spherical magnetic particles having a bulk density of 0.6 g/ml or larger.