Objective:To explore the influencing factors of acute rejection (AR) within one year after pediatric kidney transplantation (KT) and the effect of AR onset time on prognosis.Methods:From January 2011 to October 2021, a total of 112 patients aged under 18 years at the time of transplantation were selected.After excluding 6 of them with early renal non-function caused by non-rejection, 106 cases were examined.There were 63 males and 43 females with the age of 15(12, 16) years.The donors were living related (n=26) and deceased (n=80).According to the presence/absence and onset time of AR, they were assigned into three groups of AR within one year, AR after one year and non-AR.The relevant clinical data of donor/recipient, influencing factors of AR and therapeutic outcomes of AR were retrospectively compared.One-way ANOVA or Kruskal-Wallis test was utilized for comparing 1-year renal function after the occurrence of AR among three groups.With graft-function loss as an end-point event of follow-up, the effects of AR within one year and AR after one year on survival rate and function of graft-kidney were analyzed by Kaplan-Meier survival curve.Results:The median follow-up period of 106 pediatric KT recipients was 35 months.During follow-ups, 19 episodes of AR occurred in 17(16.0%) patients and 89 recipients exhibited no AR episode by the end of follow-up (non-AR group).As for initial AR, 9 episodes of AR occurred within one year (AR within one year group) and 8 episodes of AR after one year (AR after one year group).After anti-rejection treatment, 8 patients (47.1%) achieved full recovery and 6 patients (35.3%) failed to completely normalize and 3 patients (17.6%) developed graft failure.Univariate analysis indicated that, as compared with non-AR group, female recipients, donors aged under 8 years and early postoperative infection with parvovirus B19 were risk factors of AR within one year ( P=0.032, P=0.039, P=0.047).Kaplan-Meier survival analysis revealed that the incidence rates of AR within one year in patients with donors aged under 8 years and early postoperative parvoviral infection were 14.5%(8/55) and 30.0%(3/10) respectively.They were significantly higher than 2.0%(1/51) and 6.3%(6/96) of patients with donors aged above 8 years and those without parvoviral infection ( P=0.012, P=0.004).With graft-function loss as an end-point event of follow-up, Kaplan-Meier survival analysis showed that 10-year kidney graft survival rate in AR within one year and AR after one year groups were 88.9% and 65.6%.Both were significantly lower than that in non-AR group (98.9%).And the inter-group differences were statistically significant ( χ2=4.286, P=0.038; χ2=7.787, P=0.005).However, no significant difference existed in survival rate between AR within one year and AR after one year groups ( P=0.689).One-way ANOVA and Kruskal-Wallis test indicated that estimated glomerular filtration rates at 3/6/12 months after an onset of AR in AR within one year group were (76.8±51.6), (80.6±56.6) and (85.6±40.2) ml·min -1·1.73 m -2.The values of 3/6 months were lower than (125.3±39.2) and (124.7±38.2) ml·min -1·1.73 m -2 in AR after one year group.And the inter-group differences were statistically significant ( P=0.021, P=0.039).The values of 3/6/12 months were lower than (112.2±34.2), (115.3±33.2) and (117.4±30.2) ml·min -1·1.73 m -2 in non-AR group.And the inter-group differences were also statistically significant ( P=0.019, P=0.020, P=0.020). Conclusions:Female recipients, donors aged under 8 years and early postoperative infection with parvovirus B19 may elevate the risks of AR in children within one year of KT.AR within one year affects the survival rate of graft-kidney and renal function.