UNLABELLED: According to the detection of hearings ability of children in iodine deficiency areas who was born before and after iodine supplement, the effects of iodine supplement on hearing system development was evaluated. METHOD: Hearing was tested by AS-72 type pure zone diagnostic audiometer(made in Denmark). Hearing of 11-14 years old students were tested before iodine supplement in iodine deficiency areas in 1984, the control was students living in non-iodine deficiency areas. Iodine salt (50 mg/kg) were supplied by the end of 1984, the hearings of children born after one year of iodine supplied were tested in 1999. The result showed that the average hearing threshold of students before iodine supplied in iodine deficiency areas was significance higher than of non-iodine deficiency areas. The hearing of children born after one year of iodine salt supplied in deficient areas had no significant difference from that of normal areas. The development of hearing system might be deteriorated by iodine deficiency during pregnant. It was able to meet the need of iodine that pregnant women ate 1:20 thousands iodine salt.