One of the most significant impacts of afforestation with non-native species is changes in the quantity and quality of throughfall reaching the forest floor. This study investigated the effect of afforestation with non-native species of Pinus eldarica and Cupressus arizonica on the pH, electrical conductivity (EC), and concentration of some nutrient elements in the throughfall; i.e., sodium (Na+), calcium (Ca++), magnesium (Mg++), and potassium (K+), in comparison with those of Quercus brantii in the Chogha-Sabz Forest Park of Ilam. Five individual trees were selected from each species. Throughfall samples were collected using a total of 128 rainwater collectors. Eight collectors were installed in an open field as control samples, and eight collectors were placed beneath each tree across the four geographical directions. Results indicated that throughfall Ca++ concentration varied significantly between Q. brantii (2.9 mg L⁻¹) and C. arizonica (4.11 mg L⁻¹) for the third rainfall event. Analysis of the second rainfall event showed the throughfall Mg++ concentration of Q. brantii (1.31 mg L⁻¹) differed significantly from the those of C. arizonica (0.33 mg L⁻¹) and P. eldarica (0.71 mg L⁻¹). However, a significant difference was observed only between Q. brantii and P. eldarica (P<0.01). In the first rainfall event, the throughfall K+ concentration of Q. brantii (17.4 mg L⁻¹) differed significantly (P<0.01) from those of C. arizonica (5.5 mg L⁻¹) and P. eldarica (6.1 mg L⁻¹). According to the second rainfall event, K+ value of Q. brantii showed a significant difference only when compared to C. arizonica. Regarding throughfall pH, Q. brantii differed significantly only from P. eldarica throughout both for the first and second rainfall events (P<0.05). Non-native species commonly used in extensive afforestation project, not only alter the quality of water reaching beneath the trees but also change the chemical composition, EC, and pH of rainwater and these species, therefore, should be carefully selected.