Objective: To investigate the incidence and prognosis of hypophosphatemia in critically ill children treated with continuous blood purification (CBP). Methods: The medical records of the critically ill patients, who were treated with CBP, admitted to pediatric intensive care unit (PICU) of Shanghai Children's Hospital from May 2014 to April 2017 were retrospectively analyzed. The serum phosphorus levels were tested before CBP, at 48-72 h during CBP, at the end of CBP and on the next day after CBP finished. Phosphorus supplement was given to the children with severe hypophosphatemia. Results: A total of 85 patients met the inclusion criteria. The serum phosphorus levels at the 4 indicated time points were (1.4±0.5), (0.7±0.3), (0.8±0.3), (0.9±0.4) mmol/L, respectively (F=45.21, P<0.05). Among the children, 66 cases (78%) had hypophosphatemia during CBP. The incidences of moderate and severe hypophosphatemia were 32 (48%) and 9 (14%), respectively. There were 41 patients with CBP replacement rates of (35-49) ml/(kg·h), while 44 patients with CBP replacement rates of 50-70 ml/(kg·h). There were significant differences at 48-72 h during CBP, the end of CBP and on the next day after CBP ((0.8±0.4) vs. (0.5±0.2), (1.0±0.3) vs. (0.6±0.2), and (1.1±0.4) vs. (0.8±0.2) mmol/L; t=7.672, 4.060, 14.440, P<0.05). Atotal of 9 cases were treated with sodium glycerophosphate. Among the 85 children, 24 (28%) patients died while 61 (72%) survived. There were no significant differences between the two groups in serum phosphorus levels at the indicated time points ((1.4±0.5) vs. (1.4±0.5), (0.7±0.3) vs. (0.7±0.3), (0.7±0.3) vs. (0.8±0.3), and (1.0±0.3) vs. (0.9±0.3) mmol/L, respectively, P>0.05). Conclusions: Hypophosphatemia is prone to occur during CBP, which probably related to the replacement rate. There was no significant relationship between hypophosphatemia and mortality in critically ill children after giving phosphorus supplementation.