Background. The online percent coefficient of variation reporting system could monitor the variation of tacrolimus trough level (T-0) and identify kidney transplant recipients (KTRs) with a higher percent coefficient of variation (%CV) instantly. Consequently, transplant doctors and pharmacists could take actions to improve drug variability. The purpose of this study was to determine the efficacy of the system for higher intrapatient variability of To in KTRs. Methods. The To data were collected with KTRs routinely followed up at an outpatient clinic between June 2016 and November 2016. The %CV was calculated with To data within 6 months before and after the index date. The last outpatient clinic visit date was before December 1, 2016. The KTRs with %CV of To greater than 22% were enrolled. Results. The study consisted of 183 KTRs (96 male, 87 female), the median age was 50 years (interquartile range [IQR], 41.0-57.0), and the median years post-kidney transplantation was 7 years (IQR, 3.0-12.4). The median To and creatinine level at baseline were 6.09 ng/mL (IQR, 4.80-7.52) and 1.33 mg/dL (IQR, 1.03-1.72), respectively. After the intervention, the median %CV of To was significantly lower than before, 32% (IQR, 26%-42%) vs 22% (IQR, 15%-33%), P < .001. The average improvement of %CV was also significantly better in KTRs with %CV >= 30% (median, from 41% to 25%) than KTRs with %CV between 22% and 30% (median, from 26% to 20%), P < .001. Conclusions. The results of this study indicate that continuously aggressive intervention with an online %CV reporting system effectively improves intrapatient variability of To in KTRs.