Objective　To detect the peri-operative status of vitamin D and its association with postoperative clinical outcomes in children with tetralogy of Fallot (TOF). Methods　Twenty-one children with TOF were randomly enrolled. Blood samples were collected at five time points, including preoperative, immediately after surgery, 24, 48, and 72 hours after surgery. The blood 25-hydroxyvitamin D [25(OH)D] concentration was measured by liquid chromatography/mass spectrometry (LC/MS). Results　The median age of the children was 0.66 years. The baseline 25(OH)D was (25.1±9.2) ng/mL(1 ng/mL＝0.40 nmoL/L). Vitamin D deficiency rate was 19% before operation, and 81% immediately after surgery. There were significant differences of 25(OH)D concentrations at the five time points (P<0.01). However, no significant difference was showed after control of the cardiopulmonary bypass time (P>0.05). No significant difference was found among 25(OH)D level and the length of hospital stay, cardiac intensive care unit (CICU) stay, and mortality (P>0.05). Area under curve of 25(OH)D concentration was computed. There was no significant difference among the area and the length of hospital, CICU stay, and hospitalization cost (P>0.05). Conclusion　Vitamin D deficiency is common in children with TOF. Cardiopulmonary bypass significantly affects the level of 25(OH)D after surgery. Vitamin D deficiency may increase the demand for treatment of advanced antibiotics and vasoactive agents.