A monomer for a shell or a mixture of at least two monomers for a shell was suspension polymerized in the presence of core particles and a polymerization initiator to obtain polymer particles, wherein said core particles are formed of a polymer obtained by polymerization of a monomer for a core or a mixture of at least two monomers for a core and containing a colorant, wherein said monomer for a shell or mixture of monomers for a shell is one which gives upon polymerization a polymer having a glass transition temperature higher than that of the polymer forming the core particle, and wherein said polymerization initiator is represented by the following formula 1: ##STR1## wherein X.sup.1, X.sup.2, X.sup.3 and X.sup.4 independently represent oxygen atom, sulfur atom, >NR (wherein R is hydrogen atom, alkyl group, or group); R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and R.sup.6 independently represent alkyl group, aryl group, or alkyl or aryl group having at least one substituent which is --OR, --OH, --NHR, or --NR.sub.2 (wherein R is alkyl group or aryl group), and n and m independently represent an integer of 1 to 10. An outer additive was applied on the polymer particle to obtain a polymerized toner. This polymerized toner has low fixing temperature, excellent overhead projector transparency, good shelf stability, and exhibiting a less pronounced reduction in electric charge under conditions of high humidity and high temperature.