The kinetics of the ultraviolet light-induced solution atom transfer radical polymerization (ATRP) of methyl acrylate using titanium oxide (TiO2) was investigated through experiments and modeling by the method of moments. The apparent rate coefficient for activator (re)generation accounting for the variation of the amount of TiO2 was fitted to match the experimental data. The amplification experiments were then conducted to interpret and better understand the size effect on the photoATRP behaviors, of which the experimental data indicated that the polymerization rate and M-w/M-n are positively correlated with the size of the reaction volume. The simulations revealed that the termination rate coefficient (k(t)) and the deactivation rate (k(da)) diminish with the increasing size. In addition, the amplification effect was analyzed theoretically. When the size is scaled up, the heat transfer area per unit volume decreases, leading to the reduction in heat removal capacity so as to result in local overheating. The polymerization rate therefore increases with the viscosity increasing at a higher speed, causing the decrease of k(t) and k(da). As a result, the higher free radical concentration drives the polymerization toward acceleration and loss of control, consistent with the data of the amplification experiments.