Background: Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) such as palbociclib, abemaciclib, and ribociclib have changed the landscape of management of estrogen receptor-positive and HER2-negative breast cancer in recent years. We conducted a systematic review and meta-analysis of phase 3 randomized controlled trials (RCTs) to determine the relative risk of hepatic dysfunction associated with the use of CDK4/6i. Methods: We conducted a systematic search using PRISMA guidelines in PubMed, EMBASE, American Society of Clinical Oncology (ASCO) and San Antonio Breast Cancer Symposium meeting abstracts from inception through Jan 30, 2021. Phase 3 RCTs using CDK4/6i in the intervention arm and reporting the number of events for elevation of liver enzymes were included in the analysis. The Cochran-Mantel-Haenszel method and random effects model were used to calculate the pooled risk ratio (RR) with 95% confidence interval (CI). Heterogeneity was tested by Cochran’s Q test and I² value. Results: Nine phase 3 RCTs — MONALEESA-2, MONALEESA-3, MONALEESA-7, MONARCH 2, MONARCH 3, MONARCH plus, monarchE, PALOMA-2, and PALOMA-3 — randomizing 5,809 patients in the CDK4/6i arms and 4,638 patients in the control arms were included in the analysis. The CDK4/6i arms used CDK4/6i such as palbociclib, abemaciclib, or ribociclib in combination with one of the standard-of-care endocrine therapies such as letrozole, anastrozole, tamoxifen, or fulvestrant. The control arms received placebo along with respective endocrine therapies. The incidence of any grade alanine aminotransferase (ALT) elevation was 13.1% in the CDK4/6i arm and 5.4% in the control arm, pooled RR: 2.18, 95% CI: 1.74-2.72, P < 0.00001, I² = 45%. The incidence of any grade aspartate aminotransferase (AST) elevation was 12.5% in the CDK4/6i arm and 5.3% in the control arm, pooled RR: 2.00, 95% CI: 1.57-2.54, P < 0.00001, I² = 57%. The incidence of grade 3/4 ALT elevation was 4.1% in the CDK4/6i arm and 0.8% in the control arm, pooled RR: 4.43, 95% CI: 3.08-6.37, P < 0.00001, I² = 0%. The incidence of grade 3/4 AST elevation was 2.9% in the CDK4/6i arm and 0.9% in the control arm, pooled RR: 2.70, 95% CI: 1.75-4.19, P < 0.00001, I² = 29%. No fatal case of hepatotoxicity has been reported. Conclusions: Cyclin-dependent kinase 4/6 inhibitors are associated with significant risk of any grade and grade 3/4 hepatic enzymes elevation. Regular monitoring of liver function is a key to early detection and initiation of appropriate management.