Abstract: A magnetic toner for developing an electrostatic image is disclosed which has a binder resin, a magnetic material and an iron compound of the formula (I). The magnetic toner has a saturation magnetization of 20 to 50 Am.sup.2 /kg and a coercive force of 40 to 200 oersted.

Abstract: A treated silica fine powder and a toner having this powder to be used as a toner for developing an electrostatic image. The treated silica fine powder is formed of treated fine silica particles obtained by treating fine silica particles with (a) a first silane coupling agent in which at least one of a substituted secondary alkyl group, an unsubstituted secondary alkyl group, a substituted tertiary alkyl group, an unsubstituted tertiary alkyl group, a substituted cyclic hydrocarbon group and an unsubstituted cyclic hydrocarbon group is bonded to a silicon atom of the silane coupling agent, and by thereafter treating the resultant fine particles of silica with a second silane coupling agent having the formula ##STR1## wherein R1 represents a methyl group, a halomethyl group, a saturated straight chain hydrocarbon group or an unsaturated straight chain hydrocarbon group; Y represents an alkoxy group or a halogen group; m represents an integer of 1 to 3; n represents an integer of 1 to 3; and m and n are 4.

Abstract: A developer for developing electrostatic images is constituted by toner containing a binder resin and a charge controller. The charge controller comprises an arylurea compound which is an arylurea having at least one electron-attracting group or electron-donating group, or a polyarylurea including such an arylurea as a recurring unit. The arylurea compound is substantially colorless and can have stable but different levels of triboelectric chargeability depending on the substituents.