The study was conducted to evaluate the effects of dietary organic acid mixture(lactic acid 12%, formic acid 9%, citric acid 5%, butyric acid 5% and phosphoric acid 6%) on growth performance, organ weight, blood immunological parameter and intestinal villi morphology in broilers. Dietary treatments included 1) CON (basal diet), 2) OA1 (basal diet + 0.1% organic acid mixture) and 3) OA2 (basal diet + 0.2% organic acid mixture). Four hundred eighty hatched Arbor Acre broiler chickens were housed in 24 pens of 20 birds each. Eight replicate pens were allotted into each treatment by completely randomized design. Daily weight gain, feed intake and feed/gain were not significantly different among the treatments. In organ weight, that of gizzard was significantly heavier in OA2 than CON (Linear effec t = 0.034). However, those of spleen and intestine were not significantly different among the treatments. Blood immunological parameters such as RBC, WBC and lymphocyte were not significantly difference. In intestinal villi morphology, villi length was increased in OA1 compared to CON (Quadratic effect = 0.050). In conclusion, 0.2% organic acid mixture was effective to improve gizzard weight of broilers.