This paper presents a viscoelastic model of brain parenchyma which is based on the generalized Maxwell model but considers also inertial force. The proposed model is implemented in finite element method (FEM). The viscoelastic behavior of brain parenchyma was confirmed by stress relaxation tests using porcine brain parenchyma. The stress relaxation characteristics were measured at strain 0.1, 0.2 and 0.3. The strains were applied by strain rates of 0.1 (s⁻¹) and 1.0 (s⁻¹). Viscoelastic parameters were identified by solving an optimization problem using experimental data and dynamic simulations. In order to verify the consistency and quality of the experimental data and the dynamic simulation, stress relaxation simulations were performed using the identified parameters.