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.