Typha australis leaves were used as a low-cost sorbent for the removal of aspirin from aqueous solution in batch adsorption procedure. In order to estimate the equilibrium parameters, the equilibrium adsorption data were analyzed using the following two-parameter isotherms: Freundlich and Langmuir. A comparison of linear and non-linear regression methods in selecting the optimum adsorption isotherm was applied on the experimental data. Five linearized isotherm models (including four linearized Langmuir models) and two non-linear isotherm models are thus discussed in this study. The Sum of the Squares of the Errors (SSE), Chi-square () and the correlation coefficient (R²)between the calculated data and the experimental data by non-linear method were used. It was concluded that the nonlinear method is a better way to obtain the isotherm parameters and the data were in good agreement with the Langmuir isotherm model. Typha australis leaves powder can be considered as a new useful low cost natural biosorbent for      pharmaceutical product clean-up operations in aquatic system.