This study was investigated the effects of dietary supplementation of Yacon by-product powder on performance, pH, total phenol contents, DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity, TBARS, WHC, shear force, meat color, and sensory evaluation of chicken thigh meat. Broiler chicks were fed diets for five weeks containing 0% Yacon by-products powder (Control), 0.5% Yacon by-products powder (T1), 1.0% Yacon by-products powder (T2), and 2.0% Yacon by-products powder (T3). There was no significant difference in performance among treatments, but mortality was decreased in diets by the supplementation of Yacon by-product powder than that of control. The total cholesterol, LDL-cholesterol and triglyceride of control were higher than treatment groups and HDL-cholesterol and glucose of control was lower than treatment. The pH and TBARS were significantly decreased by the supplementation of Yacon by-product powder compared to the control (P<0.05). The total phenol contents and DPPH radical scavenging activity were significantly increased by the supplementation of Yacon by-product powder compared to those of the control group (P<0.05), and especially, T3 was significantly (P<0.05) more effective in improving freshness compared to other treatment groups. The WHC (water holding capacity) and shear force were not significantly different. CIE $L^*$ and $a^*$ value of treatment groups showed significantly higher value compare to the control, however, no difference in the CIE $b^*$ values was observed among treatment groups. In conclusion, a supplementation of Yacon by-product powder was effective in decreasing pH and TBARS (thiobarbituric acid reactive substance), and increasing total phenol contents and DPPH radical scavenging activity.