A charge control agent of the present invention comprises aggregate particles of an azo-type iron complex salt represented by the following chemical formula [I] in the chemical formula [I], R1—, R2—, R3—, R4—, R5— and R6— are same or different to each other, n is 0.7 to 0.99, the aggregate particles have an average particle size of 1 to 4 microns and an average particle size of a primary particulate crystalline, that is fined the aggregate particles with ultrasonic irradiation, is at most 3 microns. A toner for developing an electrostatic image comprises a resin for the toner and the charge control agent.