In this study, the effects of yacon (Smallanthus sonchifolius) leaf on the quality characteristics of cookies were examined. In order to investigate its effects, four different amounts (0%: Control, Y-0.5, Y-1.0, Y-1.5) of yacon leaf powder were added to the cookie dough. Among the physicochemical and sensory characteristics, the density and pH of the dough, spread factor, color value, firmness, consumer acceptability, and Pearson's correlation coefficients were measured. Although there was no significant difference in pH of the doughs among the groups, density significantly decreased with increasing amount of yacon leaf powder (p<0.05). While the L, a, b values, and hardness decreased significantly, DPPH free radical scavenging activity increased significantly as the content of yacon leaf powder increased (p<0.05). Overall acceptability, appearance, taste, and texture between the control and Y-0.5 groups showed no significant differences. This study suggests the possibility of yacon leaf as an ingredient that increases the functionality of cookies.