We studied the effects on the performance and intestinal health of broiler chickens who were given Macleaya cordata (M. cordata) extract alone and those given a newly developed plant extract mixture (PEM) as a natural feed additive in the diet. Total 240 Ross 308 male chicks were used in this study and divided into 4 groups of 60 chicks each. For the experimental groups, 100 ppm PEM was added to the diet of group I (PEM 100); 200 ppm PEM was added for group II (PEM 200), and 18 ppm M. cordata extract (MCE) was added for group III. Although there were no significant differences in the feed conversion ratio, carcass weight, and carcass yield, other performance variables, including body weight, body weight gain, and feed intake were significantly affected. An analysis of the data from this study showed that specified feed additives decreased the ileal inflammation score without changing the villus height in the duodenum of the chickens. In conclusion, dietary supplementation of MCE supplement alone and the effects of newly developed PEM improved the performance parameters. Moreover, it can be said that it has an intestinal inflammation-reducing effect. Thus, this supplementation may have the potential to improve intestinal health.