Objective To investigate the level of 25-hydroxyl vitamin D [25-(OH)D] in children aged 1 to 6 years in Liuzhou area,in order to provide the scientific basis for rational supplement of vitamin D (VD).Method Totally 4 560 preschool children undergoing the physical examination in the Pediatric Health Care Department of Maternal and Child Health Hospital of Liuzhou were enrolled in this study from 15th July,2016 to 14th July,2017.Serum level of 25-(OH)D was tested by the electrochemiluminescence immunoassay. Results The average level of 25-(OH)D in 4 560 children was (101.57±31.56) nmol/L,and 908 children (19.91%) were found with 25-(OH)D insufficiency and deficiency.The 25-(OH)D level in one-year-old children was much higher than that in other age groups and the serum 25-(OH) D level decreased with age in children over 2 years old (F=208.962,P＜0.001).The rates of VitD insufficiency and deficiency among children aged 4 to 6 years were much higher than those in children aged 1 to 3 years (χ²=360.878,P＜0.001).The rates of VD insufficiency and deficiency in winter and spring were significantly higher than those in summer and autumn (χ²=82.739,P＜0.001).VD supplements decreased obviously in children over 2 years old,and over 50% of 3-year-old children did not take VD supplements. Conclusions VD insufficiency and deficiency is common in children aged 4 to 6 years in Liuzhou,especially in winter and spring.So it is recommended that VD supplements should be taken in a long-term and reasonable manner.