Objective To investigate vitamin D ( VD) level and its influencing factors in 4-15-year-old children in southwest of Zhejiang province, so as to guide intervention strategy for improving VD level. Methods A total of 2 620 4 -15-year-old healthy children who visited Lishui People's Hospital for regular physical check-up between January and December 2014 were divided into 4 age groups, namely 4 -6 years (kindergarten), 7 -9 years (lower grades in primary school), 10 -12 years (higher grades in primary school), and 13-15 years (junior middle school).We randomly selected 200 children from each age group using a random number table.A survey using self-developed questionnaire was conducted to obtain information regarding diet, exposure to sunlight, and VD supplement.Serum 25-( OH) D level was measured with electro-chemiluminescence.VD nutritional status and composition, diet, sunlight exposure, VD supplement were com-pared among the groups.Results In southwest Zhejiang, the mean VD level in primary and middle school students was ( 24.76 ±8.39 ) μg/L, clinical deficiency rate was 31.5%, subclinical deficiency rate was 45.0%, and only 23.5% reached the appropriate level, which was even lower ( 14.5%) in junior middle school students.The VD deficiency rate elevated significantly along with the growth of age (P=0.036).The level of VD was positively correlated with sunlight exposure and VD supplementation, and showed significant in-ter-group differences ( all P<0.05 ) .Conclusions The nutritional status of VD is unfavorable and sunlight exposure insufficient in primary and middle school students in southwest Zhejiang province.We should encour-age students to take more outdoor activities and increase sunlight exposure to improve their VD nutritional sta-tus.Children >7 years should be given more attention to in the intervention of increasing sunlight exposure. Students with difficulties in getting adequate sunlight exposure need VD supplements.