Objective To study the serum 25(OH)D levels of 0~7 years old children in Baoji,and to provide a scientific basis for taking vitamin D reasonable. Methods A total of 1 874 patients in Children's Health Department of Baoji Second People's Hospital were selected from January 2011 to June 2014.1 005 were male,869 were female.Using the high performance liquid chromatography - tandem mass spectrometry which was international advanced methods,serum 25(OH)D levels were determined of all the children. Results 1)The average level of serum 25(OH)D in 0～7 years old children in Baoji was (21.02±13.27) ng/ml,there were 996 children (53.15%) lake of serum 25(OH)D,390 children (20.81%) shortage in serum 25(OH)D,the value of serum 25(OH)D in zero month children was minimum,that in 3 years old children was maximum.2)The level of serum 25(OH)D was in ascending order form downtown,Chen-cang area,surrounding counties and the field.3)The levels of serum 25(OH)D in summer and autumn were significantly higher than those in spring and winter,and children's deficiency rate and inadequate rate of serum 25(OH)D in summer and autumn were significantly lower than those in spring and winter.4)The values of serum 25(OH)D in overweight and non-overweight children were (24.67±10.61)ng/ml and (20.11±11.57)ng/ml,the values of serum 25(OH)D in obese and non-obese children were (25.37±10.25)ng/ml and (20.56±10.74)ng/ml,there were significant differences in the serum 25(OH)D content between the two groups.5)Here was no significant difference in the serum 25(OH)D content between different sex. Conclusion The general lack of serum 25(OH)D exists in 0~7 years old children in Baoji area,the positive and effective measures should be taken for vitamin D supplement in 0~7 years old children.