A total of 360 one-day-old broiler chicks were randomly assigned to four treatments with five replicate cages and 18 birds per cage for a 35 d trial to investigate the effects of supplementing Achyranthes japonica Nakai (AJN) root extract in low crude protein (CP) diet on growth performance and carcass traits. Experimental diets were divided as standard CP content diet, low CP content (LCP) diet, and LCP diet supplemented with 0.025% or 0.050% AJN root extract. Dietary CP reduction impaired growth performance and carcass traits, whereas supplementing AJN root extract improved growth performance and carcass traits.