Abstract: OBJECTIVE To investigate the correlation between levels of serum 25-(OH)D and children with type 1 diabetes mellitus and diabetic ketoacidosis(DKA). METHODS Fifty-two cases who initially fell ill with type 1 diabetes mellitus were selected from 152 cases who stayed in our hospital from January 2006 to November 2009. The other 100 children were excluded from type 1 diabetes mellitus according to following standard. Clinical and laboratory data of 52 cases with type 1 diabetes mellitus was studied. The relationship between levels of serum 25-(OH)D and children with type 1 diabetes mellitus and DKA was acquired. RESULTS The serum 25-(OH)D level of children with type 1 diabetes mellitus was(63.67±28.41)nmol·L^-1 which was significantly lower than that excluded from type 1 diabetes mellitus(P<0.05). The average serum 25-(OH)D level of DKA children was (58.63±27.79)nmol·L^-1 which was statistically lower than non-DKA cases. CONCLUSION The low level of serum 25-(OH)D maybe increase the risk of development of type 1 diabetes mellitus and DKA.