Abstract: Objective To understand the iodine level and prevalence of thyroid diseases in residents in areas using iodized or non-iodized salt in Daishan, Zhejiang province. Methods In July 2010,the survey was conducted in Nizhi community(non-iodized salt area) and in Wojingtan community(iodized salt area). The concentrations of iodine in water samples and in edible salt samples were detected. The detections of urine iodine and blood iodine and B ultrasound examination of thyroid were conducted for 707 people from 483 families in non-iodized salt area and in 117 people from 87 families in iodized salt area. Results The median of iodine in water was 17.5 μg/L. The qualified rate of iodized salt was 65.38% and the coverage rate of iodized salt was 79.49% in iodized salt area. The median of urine iodine concentration in residents in non-iodized salt area was 117.06 μg/L,which was lower that in iodized salt area(182.57 μg/L). The prevalence rates of clinical hyperthyreosis, subclinical hyperthyreosis, clinical hypothyroidism and subclinical hypothyroidism were 0.28%, 0.42%, 0.71% and 2.97% respectively in non-iodized salt area and 0, 0.85%, 0.85% and 8.55% respectively in iodized area. The prevalence rate of subclinical hypothyroidism in iodized salt area was significantly higher that in non-iodized salt area, the differences in other rates had no significance. The prevalence rate of thyroid nodule was 27.58% and 34.19% respectively in two areas, and the TPOAb positive rate was 8.35% and 12.82% respectively, the TGAb positive rate was 6.79% and 5.13% respectively. The differences had no statistical significances. Conclusion The iodine level of the residents in iodized salt area was normal. The differences in the prevalence of thyroid diseases, except subclinical hypothyroidism, had no statistical significances, reflecting that using iodized salt hadn't increase the prevalence of thyroid diseases. The iodized salt coverage and the resident iodine level in non-iodized salt area were at normal but low level. It is necessary to strengthen the promotion of iodized salt using and continue the strategy of reasonable supplement of iodine.