A batch experiment was conducted to study the sorption of phenanthrene onto Al (oxy)hydroxides formed under the influence of tannic acid. The sorption isotherms were employed to describe the sorption behavior. Linear and nonlinear regression methods were compared to select the optimal isotherm. Results showed that significant sorption of phenanthrene occurred on the surfaces of all Al (hydro)oxides, but the sorption capacity didn’t completely conform with tannic acid content and crystal form. Results generated with linear regression showed some uncertainties, indicating that linear regression was not good to determine the best fitting isotherm. In contrast, nonlinear regression was found to be better to obtain the parameters involved in the isotherms and also the optimal isotherm. By comparing R2 and χ2 values, the optimal isotherm for sorption of phenanthrene onto different Al (oxy)hydroxides with different tannic acid/Al molecular ratios (MRs=0, 10-3 ,10-2, 10-1 ) were Freundlich, Freundlich, Dubinin-Radushkevich and Freundlich isotherm, respectively, which implied the heterogeneity of Al (oxy) hydroxides surfaces. Modified Freundlich isotherm was adopted to compare directly phenanthrene sorption characteristics of different Al (oxy)hydroxides formed under the influence of tannic acid and found the sorption capacity increasing with the order of MR=10-3＜MR=10-2＜MR=0＜MR=10-1. We deduced that phenanthrene sorption is entropy-driven.