The geometric size effects (GSEs) of Lemaitre damage model parameters (the critical damage value at rupture, D_c, the strain at the damage threshold, ε_D, and the strain at rupture, ε_R) of a rolled CuAl5 alloy were evaluated using uniaxial tensile experiments and the finite element method. The results indicated the presence of size effect on the damage model parameters of the rolled CuAl5 alloy. With an increase in reduction ratio (R_r) at a constant thickness (t), D_c increased; with an increase in t at a constant R_r, D_c decreased and then increased. Both ε_D and ε_R decreased with increasing R_r and decreasing t. New models of the relationship between the damage model parameters and t were established for the three R_r values. The predicted results of the models agreed with the experimental ones. These results help to accurately predict the fracture behavior of microparts during plastic forming.