A toner for developing an electrostatic image is constituted by a composition containing a binder resin component and a coloring agent, wherein the binder resin component contains a low-molecular weight component having a molecular weight of at most 5.times.10.sup.4 and a branching index g' of below 1. The low-molecular weight polymer component is preferably obtained by polymerizing a second monomer in mixture with a prepolymer in the presence of a polymerization initiator comprising a peroxide having a functional group of: ##STR1## and mixed with a high-molecular weight polymer component obtained by polymerization in the presence of a poly-functional polymerization initiator, and a low-molecular weight wax. The resultant toner is characterized by a good balance between the fixability and anti-offset characteristic.