OBJECTIVE： To investigate the effects of blood concentration monitoring of cylosporin A （CsA） in patients with nephrotic syndrome （NS） on efficacy and safety. METHODS： The medical records of 154 NS patients receiving CsA and blood concentration monitoring in nephrology department of China-Japan Friendship Hospital during Jan. 2014-Aug. 2017 were analyzed retrospectively. The results of blood concentration monitoring in 63 adult inpatients with refractory NS receiving CsA for the first time within 6 months of initial treatment were analyzed statistically. The relationship of blood concentration monitoring with efficacy and safety was analyzed. RESULTS： The blood concentration of CsA in 154 patients were monitored for 512 times with an average of 3.32 times/person， and average blood concentration was （125.98±105.13）ng/mL. The patients with blood concentration of CsA＜100 ng/mL accounted for 44.14％. There was no statistical significance in average monitoring times or average blood concentration between male and female， average blood concentration of CsA among different age groups （P＞0.05）. The blood concentration was monitored for 237 times in 63 adult inpatients with refractory NS receiving CsA for the first time within 6 months of initial treatment （induction period）. Average blood concentration of effective group were significantly higher than ineffective group； the proportion of effective group with blood concentration＜100 ng/mL was significantly lower than that of ineffective group， with statistical significance （P＜0.05）. Among 63 patients， 17 patients suffered from ADR （the incidence of ADR was 26.98％）. The average blood concentrations of ADR patients were significantly higher than those without ADR； the monitoring times of ADR patients with blood concentration＞150 ng/mL was significantly higher than those without ADR， with statistical significance （P＜0.05）. There was no statistical significance in the incidence of ADR between effective group and ineffective group （P＞0.05）. Among effective group， there was no statistically significance in average blood concentration between ADR patients and patients without ADR （P＞0.05）； the monitoring times of ADR patients with blood concentration＞150 ng/mL was significantly higher than patients without ADR， with statistical significance （P＜0.05）. With the increase of monitoring times， the incidence of ADR decreased gradually. There was no statistical significance in the incidence of ADR among patients who were monitored for different times （P＞0.05）. CONCLUSIONS： The pharmacokinetics of CsA varies in different patients and many factors affect its blood concentration. The changes of blood concentration affect the efficacy and safety of CsA. It is difficult to determine the dosage of CsA based on experience in the treatment of NS with CsA. Great importance should be attached to blood concentration monitoring of CsA and the implementation of individualized dosage regimen based monitoring results so as to improve therapeutic efficacy and reduce the occurrence of ADR.