This experiment was designed to investigate the effects of supplementation with plant extract, either alone or in combination with an organic acid on growth performance, intestinal organ measurements and intestinal microbiology. One-day-old male Ross 308 strain broiler chicken (n=96) were allocated to 4 dietary treatments in a randomized complete block design. Dietary treatments were: (i) basal diet (as a control) (C), (ii) basal diet + organic acid mixture feed (OA), (iii) basal diet + plant extract (PE) and (iv) basal diet + organic acid mixture + plant extract feed (OA+PE). Body weight gain (BWG), feed intake (FI) and feed conversion ratio (FCR) were not improved by supplementation of OA or PE to the diets. Proventriculus, gizzard, hearth, liver, pancreas, abdominal fat and bursa of Fabricious weights were not significantly affected by dietary treatments. OA and PE diets resulted in increased weight and length of duodenum, jejenum, ileum and caceum. However, differences between treatments were not statistically significant (P>0.05). Supplementation of organic acid has positive effect on ileal microbiology. In ileal digesta, LAB and yeast counts were significantly (P<0.001) increased for birds fed OA and PE, whereas Escherichia coli counts were significantly (P<0.001) decreased in OA group. In conclusion, as OA and PE supplementation had any positive effects on the performance. Ileum microflora of OA supplemented group changed for the benefit of non-pathogenic bacteria, probably due to the decrease in pH levels of ileum. E. coli count was found lower for OA treatment than the other groups. These results indicate that the OA can improve gut health. The products that researched show promising effects, however, further researchers may be useful to understand their effects better.