Background: Breast cancer is a global health concern, affecting many women. Various treatment approaches to breast cancer treatment have been developed, including CDK4/6 inhibitors which can block CDK4/6 and have shown great effectiveness. CDK4 is a specific CDK involved in the G1 phase of the cell cycle. This study aims to investigate the correlation between CDK4 and Ki67 (a marker of cell growth) in breast cancer. By this study, researchers hope to gain new insights into breast cancer and develop effective treatment strategies. Materials and Methods: CDK4 and Ki67 immunostain was performed on 73 paraffin blocks of patients with breast cancer who had not undergone chemotherapy. Mann-Whitney tests were used to analyze the data, which were then summarized in tables using SPSS 27 software. Results: There were 62 samples (84.9%) stained with CDK4 and 11 samples (15.1%) unstained with CDK4. There were 35 samples (47.9%) with high Ki67 and 38 samples (52.1%) with low Ki67. Mann Whitney test showed a significant association between CDK4 and Ki67 (p=0.009). Conclusion: CDK4 increases when Ki67 increases, so these biomarkers can be used to predict a better prognosis and as targeted treatment strategies for breast cancer therapy in the future.