Objective: To identify the prevalence of Vitamin D deficiency (VDD) and related factors in children aged 12- 36 months at some kindergartens in Gia Loc district, Hai Duong province. Method: 2 kindergartens were randomly selected in Gia Loc district. Total of 263 children aged 12- 36 months were measured body weight, height, and venous blood to analyze serum concentration of 25(OH)D. Their mothers were interviewed about educational level, occupation and related factors by structured questionaire. A child was classified as having VDD if her/his 25(OH)D concentration was 50 nmol/L, and vitamin D insufficience if 50 nmol/L or