Objective: 17-37% of patients with metastatic hormone receptor (HR)-positive breast cancer have metastases only to bone. The present study aimed to compare the CDK4-6 inhibitors palbociclib and ribociclib in terms of their efficacy in treating HR-positive human epidermal growth factor receptor 2 (HER2)-negative breast cancer patients with only bone metastases detected at diagnosis. Material and Methods: The study was conducted as a retrospective observational study of 31 patients with HR-positive and HER2-negative breast cancer and only bone metastases who were treated with CDK4-6 inhibitors. The patients were divided into two groups based on the CDK4-6 inhibitor used and subjected to overall survival (OS) analysis. Results: The median age of the patients included in the present study was 57 years (36-76). The median OS in the ribociclib group was 25.46 months (confidence interval was not reached in the Kaplan-Meier analysis). The median OS in the palbociclib group was 16.07 months (95% CI: 7.88-24.25). The difference in OS between the two groups was statistically significant (p=0.043). Among the other variables with the potential of affecting the OS of these patients, the N stage and survival values were observed to be significantly different (p=0.033) between the two groups. The multivariate analysis revealed the N stage (p=0.011) and the type of CDK4-6 inhibitor used (p=0.023) as the independent risk factors that affected the OS of these patients. Conclusion: In patients with hormone-positive HER2-negative breast cancer with only bone metastasis, ribociclib administration achieved increased OS compared to the use of palbociclib.