The kinetics and mechanism for the synthesis of core-shell styrene-butyl acrylate was studied in this research using two methods: the first involved determining the number of polymers produced as a solid content with respect to time; the second consisted of determining the unreacted monomer concentration with respect to time with gas chromatography (GC). Based on the reaction rate equation obtained from the experiment, the equation for the reaction rate for each stage can be predicted. The order of styrene in the core-shell synthesis calculated from the experiment is supported by the estimation of the derived reaction mechanism. The order of the ammonium persulphate (APS) initiator and the order of the sodium lauryl sulphate (SLS) surfactant, obtained from the experiment, are not suitable for the estimated mechanism, which caused initiators and surfactants to play roles only in the first step of the reaction, at the time of core formation or during nucleation. The order of butyl acrylate in the styrene core grafting obtained from the experiment is supported by the result of the mechanism estimation that is thus derived.