In this work, the reaction kinetics of p-nitrophenol ozonation in a bubble column at low pH of water was studied. The reaction kinetic parameters, rate coefficients, and stoichiometric coefficients were estimated by using nonlinear optimization. The reaction rate equations were written by applying a part of the reaction scheme of Yu and Yu (Ozone Sci. Eng. 2001, 23, 303-312). The concentration of the unknown intermediate compounds is presented as a residual COD (chemical oxygen demand) calculated from the measured COD and the theoretical COD for the known species. The decomposition rate of p-nitrophenol on the pathway producing hydroquinone was found to be about two times faster than the decomposition rate on the pathway producing 4-nitrocatechol. The ozone self-decomposition by hydroperoxide ions seems to be the plausible cause for the relatively high ozone consumption at low pH. The identifiability and reliability of the estimated parameters were analyzed with the Markov chain Monte Carlo (MCMC) method. MCMC methods are Bayesian statistical methods that can be used for analyzing the distribution of parameters in nonlinear models in order to extend and support the information given by traditional regression analysis.