The nonlinear dynamic equations introduced by Biot to model poroelastic media have not been implemented to describe nonlinear acoustic waves in such media. The equations of the semilinear Biot model are revised and a mathematical model depicting the physical nonlinearity is established. A perturbation technique is then applied to find solutions to the nonlinear Biot equations. The computational results are carried out in details for a one-dimensional model in which the contributions of the fast and slow compressional waves into second harmonic wave are analyzed. The correlation between second and third-order Biot coefficients and measurable nonlinear parameters is also presented along with a parameter analysis.