This study was conducted to investigate the effects of acorn (fruits of Quercus species) powder on the antioxidant activity and quality characteristics of cookies. Cookies were prepared with different amounts (0, 0.5, 1, 3 and 5% to the flour quantity) of acorn powder. The antioxidant activity was estimated by DPPH free radical scavenging activity and the total phenolic acid content in acorn powder and cookies. For analyzing quality characteristics, bulk density, pH of the dough, spread factor, loss rate, leavening rate, color, texture profile analysis, and sensory evaluations were measured. The moisture contents, a values, total phenolic acid content and DPPH free radical scavenging activity of cookies significantly increased with increasing acorn powder (p<0.001), while the pH of the dough, L values and b values of the cookies significantly decreased with increasing acorn powder (p<0.001). The consumer acceptability score for the 3% acorn cookie groups ranked significantly (p<0.05) higher than the other groups in overall preference, appearance, flavor, taste and color. From these results, we suggest that acorn is a good ingredient for increasing the consumer acceptability and the functionality of cookies.