An object of the present invention is to provide a polymerized toner which has low-temperature fixing ability and is not likely to leak the toner from a developing cartridge, especially, when the toner is used for a high-speed image-forming device. A polymerized toner produced by polymerizing a polymerizable monomer composition comprising a polymerizable monomer, a colorant and a release agent in an aqueous medium is used, wherein: (1) the release agent is an ester compound; (2) the release agent is in the content from 1 part by weight or more to 9 parts by weight or less per 100 parts by weight of a monovinyl monomer in the polymerizable monomer; (3) a maximum endothermic peak temperature in a DSC curve of the release agent is in the range from 55° C. or more to 90° C. or less; and (4) a melt index value of the polymerized toner at 150° C. under load of 98 N (10 kgf) is in the range from 1 g/10 min or more to 30 g/10 min or less.