AIM: To explore the intra-patient variation of tacrolimus concentration in children with nephrotic syndrome, evaluate clinical efficacy and analyze the factors, in order to provide reference for promoting rational drug use in children. METHODS: Sixty-four children with nephrotic syndrome were followed up in our hospital from January 2021 to November 2023. Basic information, medication orders, tacrolimus concentration and CYP3A5*3 polymorphism were collected. Evaluate the clinical efficacy and analyze the factors affecting tacrolimus concentration intra-patient variation. RESULTS: Tacrolimus initial dose was 0.01-0.14 mg·kg-1·d-1. C0 was (4.42±3.03) ng/mL, only 15.63% of children in the target concentration. After medication adjustment, children in target concentration up to 62.07%. 50% and 52.17% of children reach the target concentration respectively at 3 and 6 months. The coefficient of variation (CV) about all Tac-C0 was 37.75%±16.16%. The overall remission rate was 89.58%. The CV of children with non-remission was significantly higher (P<0.05). Tac-C0-CV was affected by CYP3A5*3 polymorphism and age (P<0.05). CONCLUSION: Children with high CV have poor clinical efficacy. The Tac-C0-CV in children with nephrotic syndrome is affected by CYP3A5*3 and age. TDM and genotype testing should be paid more attention in order to adjust the medication.