AbstractThe variation in vitamin D status is still unclear. We aim to describe the vitamin D status among healthy infants and children in Shanghai (31° N latitude), one of the largest cities in China. We conducted a hospital‐based, 2‐year retrospective observational study and recruited children for health examination at the Tongren Hospital affiliated with Shanghai Jiao Tong University School of Medicine from January 2019 to December 2020. Serum 25‐hydroxyvitamin D (25(OH)D) levels were measured using an enzyme‐linked immunosorbent assay. A total of 6164 children aged 0–11 years were included. Of these, 94.4% of the serum 25(OH)D measurements at first assessment were within the range of 12–50 ng/mL. The median 25(OH)D level was 31.3 (IQR 25.6, 38.1) ng/mL, the percentages of 25(OH)D < 20 ng/mL and 25(OH)D < 30 ng/mL were 10.0% and 43.8%, respectively. Low vitamin D status (deficiency and insufficiency) differed significantly by age group (infants, toddlers, preschoolers, and schoolers) and seasonality (allp< .001), but not by gender. For the sub‐group (n= 855) of children with repeated assessments, their low 25(OH)D levels increased significantly whether after about a 7‐month (n= 351) or 12‐month (n= 504) interval, and the increments of median 25(OH)D levels were 8.1 ng/mL and 2.1 ng/mL respectively (p< .001). This study documents the vitamin D status in Shanghai, showing that low vitamin D status is common in infants and children and suggesting that the assessment of 25(OH)D level is necessary for individuals who are at risk for deficiency or excess.