The photopolymerization kinetics of poly(urethane-acrylate)/zirconia (PUA/ZrO2) nanocomposite coatings were monitored on-line and in-real-time with microdielectrometry (DEA) in terms of logarithmic ion viscosity (log). For comparison, real-time infrared spectroscopy (RTIR) was also employed to determine the evolution of C=C bond conversion (C) with irradiation time (t). Coupling log-t curves with C-t curves indicates that the relationship between log and C for all the coatings with different formulations (i.e. the type of photoinitiator, ZrO2 content) and curing condition (i.e. irradiation intensity) can be correlated to one linear equation at conversion less than ∼85%. Moreover, DEA monitoring was longer time to reach polymerization equilibrium than RTIR for those cases with high limited conversion, suggesting that the former is more sensitive to C=C bond conversion than RTIR at high conversion stage (C>∼85%). DEA monitoring on the photopolymerization kinetics of PUA/ZrO2 coatings as a function of various parameters further demonstrates that DEA results are reliable and reasonable to conventional radical photopolymerization. It is believed that DEA technique will be useful not only on the optimization of curing condition but also for the formulation of UV-curable coatings.