The present invention provides a stabilizer containing, as a main component, a bisphenol monoester and a bisphenol-based compound, wherein the area of the bisphenol-based compound is 0.15 to 70 when the area of the bisphenol monoester is set to be 100 in a chromatograph obtained by liquid chromatography analysis of the stabilizer, a method of manufacturing the same, a thermoplastic polymer composition containing the stabilizer, as well as a stabilizer that can further improve the process stability of the thermoplastic polymer, as compared with the conventional one, by compounding the stabilizer into the thermoplastic polymer through a method of stabilizing the thermoplastic polymer using the stabilizer and a method of manufacturing the stabilizer.