This study was conducted to investigate the effects of acorn ($Quercus$ autissima carruther) powder on the antioxidant activity and quality characteristics of cookies. Cookies were prepared with different amounts of acorn powder (at ratios of 0, 0.5, 1, 3 and 5% to total flour quantity). Antioxidant activity was estimated based on DPPH free radical scavenging activity and total phenol content in acorn powder and cookies. To analyze quality characteristics, bulk density, pH of the dough, spread factor, loss rate, leavening rate, color, texture profile analysis, and sensory evaluations were measured. Loss rate, a values, total polyphenol contents and DPPH free radical scavenging activity of cookies significantly increased with increasing acorn powder content (p<0.01), whereas pH of the dough, L values and b values of the cookies significantly decreased with increasing acorn powder content (p<0.01). The results of sensory evaluation (appearance, taste, flavor, texture and overall preference) demonstrate that the 3% acorn cookie group showed the highest degree of preference among all items of added acorn powder. From these results, we suggest that acorn is a good ingredient for increasing the consumer acceptability and functionality of cookies.