In this study, efforts were focused on the dose-responses of the operating parameters (i.e. different processing methods (extruded/non-extruded), additives (tomato powder, buckwheat powder and rice powder), and extracts concentrations (0, 3, 6, 12, 30, 60 (mg/mL))) on the hydrogen peroxide scavenging, superoxide anion scavenging and reducing power of methanol extracts of the extrudates. The experiment is a 2 x 3 x 6 factorial design. Samples of each treatment were collected and the hydrogen peroxide scavenging, superoxide anion scavenging and reducing powers were measured and analyzed, using the one-way variance analyses (ANOVA) of the SPSS 9.0 software package. Experimental results indicated that: (a) The extrudates with tomato powders had the highest hydrogen peroxide scavenging ability, extrudates with buckwheat powders had lower, and the extrudates with the rice powders had the lowest ability. However, the antioxidative ability of the extrudates with buckwheat powders and rice powders decreased with increasing reaction time, except the extrudates with tomato powder (b) The extrudates with tomato powders and rice powders had the best superoxide anion scavenging ability, however, the extrudates with buckwheat powders had the lowest (c) The extrudates with tomato powders had the highest reducing powder ability, followed by the extrudates with buckwheat powders, whereas the extrudates with the rice powders had the lowest ability (d) The extrudates with tomato powders had a better antioxidative abilities than the others additives and (e) There was no significant difference between the hydrogen peroxide scavenging ability and the reducing power ability by different processing methods, except the products after extrusion had a better and significant superoxide anion scavenging ability.