A study was carried out to investigate the effects of organic acid mixture as well as two methionine supplements on performance, carcass characteristics and weight of gastrointestinal tract in broiler chickens. Six hundred unsexed day-old Ross 308 broiler chicks were utilized in a factorial arrangement of treatments (3×2) based on Completely Randomized Design (CRD) of 4 replicates of 25 chicks each. a Chicks were placed in floor pens (1.2 ×2 m2). Experimental diets consisted of three levels of organic acid mixture consisting of formic, lactic, malic, citric, tartaric and ortho-phosphoric acid (under the trademark Orgacid) (0, 0.5, and 1%) and two sources of methionine supplement (DL-methionine and liquid methionine hydroxy analogue (Alimet). The experiment was carried out in two periods. Levels of 0.5 and 1% of organic acids mixtures increased body weight and improved feed conversion ratio (P<0.05) during all the periods. During the grower period Alimet increased carcass weight as compared with DL-methionine. Levels of 1% of organic acid mixtures increase carcass weight as compared with other levels in starter (P<0.05). Also in this period breast weight was significantly increased by 0.5 and 1 % of organic acids mixture compared with that at 0% level (P<0.05). Abdominal fat was significantly increased by 1% organic acid mixture compared with that of 0.5% at 21 days of age. The use of organic acid at 1% level resulted in decreased in cecum weight at 21 days of age compared with that at the level of 0% (P<0.05). Intestinal length (by 0.5 and 1 % of organic acid mixture) significantly increased as compared with those at 0% level (P<0.05). Application of organic acid in general, increased carcass weight, breast weight, intestine length while decreasing weight of cecum at 21 days of age. Alimet increased carcass weight as compared with DL-methionine.