Abstract: Objective To study the serum vitamin D levels in children who were send to PICU because of infection, analyze the relationship between vitamin D levels and disease outcome and explore its clinical significance. Methods Three hundred and seventy-eight cases of patients who were sent to PICU because of infection were included, and the main types of infection were ensured when they hospitalized. The 25-(OH)D level in serum was detected and compared with 350 cases of healthy children, who come to body check or vaccination in our outpatient service at the same term. Meanwhile, PICU patients were divided into two groups according to their 25-(OH)D level:normal 25-(OH)D group 264 cases and lack 25-(OH)D group 114 cases. General condition, hospital length of stay (HLOS), PRISM score and prognosis were compared between the two groups. Results The main infection that cause children hospitalized into PICU were septic shock, serious respiratory or digestive system infection. Serum 25-(OH)D in PICU children (63.5±19.9) nmol/L was lower than healthy children (76.8±17.1) nmol/L (P<0.01), and the ratio of 25-(OH)D lacking (30.2%) was also higher than healthy children(18.6%), P<0.05. In PICU patients, lack 25-(OH)D group children were elder than normal 25-(OH)D group (P<0.01). HLOS was longer in lack 25-(OH)D group (P<0.01). But 25-(OH)D level was neither related to PIRSM score (P>0.05) nor correlated to children death (P>0.05). Conclusion Children hospitalized into PICU because of infection are lacking 25-(OH)D obviously, lack of 25-(OH)D leads to slow recovery of infection diseases, but does not affect the severity of diseases or mortality in children.