The objective of this work was to study in vivo the efficacy of various types of acids and some commercial products such as Acid pack 4 way, Salkile or Fermacto to minimize or inhibit colonization of S.typhimurium in broiler chicks. Cecal colonization with S.typhimurium was slightly affected by dietary propionic acid or formic acid, but the use of salkile "Bio-Add" was a useful means. to protect broilers from S.typhimurium colonization. There was no significant difference in cecal pH or body weight gain among acids treated groups of chicks. Acid pack 4 way "Probiotic" caused significant decrease in the colonization rates and more gain body weight. Feramacto treated feeds has little significant effect on rates of colonization, but the mean body weight of chicks was significantly increased. The best overall result was achieved with treatment with both Acid pack 4 way plus lactose. The colonization rates of combined treatment groups were discussed in details.