A yellow toner for developing an electrostatic image contains yellow color toner particles having at least a binder resin and a yellow colorant, and an external additive. The binder resin has a polyester resin having an acid value of from 2 mg KOH/g to 25 mg KOH/g and a glass transition temperature of from 52.degree. C. to 65.degree. C. The yellow colorant is a compound represented by the following Formula (I): ##STR1## The external additive is composed of a fine titanium oxide powder or fine aluminum oxide powder subjected to hydrophobic treatment. The powder has an average primary particle diameter of from 0.01 .mu.m to 2 .mu.m. The yellow toner has a weight average particle diameter of from 3.0 .mu.m to 15.0 .mu.m.