In this paper, cohesive zone parameters for an automotive structural adhesive has been extracted using numerical simulations in conjunction with experimental observations by the inverse method. In this regard, DCB specimens are fabricated according to the ASTM D2651 by AL6061-T6 adhereds and AV138 epoxy brittle adhesive in five different thicknesses, 0.2, 0.4, 0.6, 0.8 and 1.0 mm. The experimental tests are conducted as mentioned in ASTM D5528. In order to obtain the more appropriate method to calculate the fracture energy of the brittle adhesive as a critical parameter of the inverse method, a comparative investigation is employed between MBT, CBBM, Penado, Xie and Mao theories. The results reveal that CBBM, as an experimental data reduction procedure, would be the appropriate one in this case. After obtaining the other cohesive parameters utilizing bi-linear cohesive law, the numerical data indicate that the CZM results are in a good agreement with those obtained in the experiments. Finally, in order to achieve the maximum strength of the adhesive joints, an optimum range of adhesive thickness close to 0.4 mm is observed.