Abstract: A non-magnetic one-component toner developer for use in electrophotographic processes having a particle size distribution represented by the following expressions: d.sub.1 /d.sub.50 =0.32.about.0.55; d.sub.50 /d.sub.90 =0.50.about.0.70; and d.sub.50 =5-15.mu., wherein d.sub.1, d.sub.50, and d.sub.90 represent diameters of toner particles when the percentiles by volume or by weight of toner developer of that diameter are 1%, 50%, and 90%, respectively. The non-magnetic one-component toner developer disclosed in the present invention has a triboelectricity greater than 1.5 .mu.C/g, a bulk specific gravity than 0.36, and a compression ratio less than 0.24, and exhibits excellent triboelectrification characteristics and flowability, as well as provides uniformly clear images without foggy background.