This experiment was carried out to study the effect of iodine on the microbial load of drinking water of broilers as well as on their performance. The experiment was done on 300 Arbor acres one-day-old chicks, the chicks were classified into 6 groups "Aj, Bj, A2, B2, A3 and B3" each of 50 birds at the age of 21 days, the group A1 and B2 drink water contains 10 ppm active iodine, while group A3 and B3 drink water contains 25 ppm active iodine, but group Al and B1 were left without treatment. The groups Aj, Az and A3were vaccinated against ND (booster dose at 37 day old) while group B,, Bz and B3 were left without revaccination. The obtained results revealed that the birds drank water containing iodine showed high performance, general healthy conditions and low incidence of infections as compared to those drank water free from iodine.