A developer for electrostatic electrophotography which comprises a composition of colorant particles, an electric charge supplying agent and a resin binder dispersed in a dispersion medium. The resin binder is a copolymer which has a polyoxyethylene units at side chains thereof, so that the interaction with the electric charge supplying agent is improved. The resultant developer ensures good resolution, gradation and fixing property and is suitable for wet development to give high-quality images. When the copolymer used as the resin binder has styrene units therein, its solubility in the dispersion medium is improved. The developer is either liquid or solid depending on the type of dispersion medium.