Abstract： Objective:To investigate the effects of normal iodized salt diet on urinary iodine concentration and iodine uptake rate in patients with differentiated thyroid cancer (DTC) before 131I treatment. Methods:A prospective study was conducted on patients with DTC (59 male patients and 130 female patients, age (43.7±12.2) years) who received 131I treatment for the first time after total thyroidectomy in the First Affiliated Hospital of Zhengzhou University between January 2021 and April 2022. Patients were divided into normal iodized salt diet group and limited iodized salt diet group according to whether iodized salt diet was administered 4 weeks before 131I treatment. The age, gender, urinary iodine concentration, iodine uptake rate and tumor risk stratification of the two groups were compared by independent-sample t test or χ2 test. In addition, according to the concentration of urinary iodine, patients were divided into group a1 (urinary iodine <200 μg/L) and group a2 (urinary iodine ≥200 μg/L). Logistic regression analysis was used to analyze the factors affecting urinary iodine concentration. Results:The urinary iodine concentration of normal iodized salt diet group was not significantly different from that of non-iodized salt diet group ((140.53±76.66) vs (121.74±74.64) μg/L; t=1.67, P=0.489). The iodine uptake rates at 2 h, 4 h and 24 h in the 2 groups were (3.77±1.06)% vs (3.42±0.97)%, (3.33±1.07)% vs (3.21±1.15)%, (2.90±2.60)% vs (3.23±2.94)%, respectively ( t values: 2.33, 0.68, -0.81, all P>0.05). There were no significant differences in age ( t=0.56, P=0.889), gender ( χ2=1.33, P=0.250) and tumor risk stratification ( χ2=0.14, P=0.709) between the two groups. Logistic regression analysis showed that tumor risk stratification was associated with urinary iodine concentration (odds ratio ( OR)=3.914, 95% CI: 1.505-10.176; P=0.005). Conclusion:Normal iodized salt diet may have no effect on urinary iodine concentration and iodine uptake rate of patients with DTC before 131I treatment.