This study examined the effects of adding four different amounts (0%: control, 4%: M-4, 8%: M-8, 12%: M-12) of button mushroom (Agaricus bisporous) powder on the quality characteristics of cookies. The bulk density and pH of the dough, and firmness, color, spread factor, consumer acceptability of cookies, and total phenol compound content and free radical scavenging activity of mushroom powder and cookies were measured. While the bulk density and pH of the dough as well as spread factor of the cookies significantly decreased, the firmness, L values and total phenol compound contents and free radical scavenging activity of the cookies significantly increased with increasing mushroom powder content(p<.05). The consumer acceptability scores for the button mushroom cookie groups ranked significantly(p<.05) higher than those of the control group in general acceptability, appearance, flavor, color, taste, and texture. This study suggests that button mushroom powder is a good ingredient for increasing the acceptability and functionality of cookies.