The study examines the effect of diversification on the financial performance of private commercial banks in Ethiopia. The main objective is to investigate how different dimensions of diversification namely income diversification, asset diversification, loan portfolio diversification and investment diversification affects financial performance measured by Return on Assets (ROA). The study adopts a quantitative research approach and employs both descriptive and explanatory research designs. Secondary data were collected from audited annual reports of ten selected private commercial banks and official sources covering a ten-year period from 2015 to 2024. A balanced panel dataset was constructed to enable a comprehensive analysis of the relationship between diversification and financial performance over time. Descriptive statistics are used to summarize the characteristics and movements of the variables, while panel data regression techniques including pooled Ordinary Least Squares (OLS), fixed effects, and random effects models are employed to estimate the relationship between diversification and financial performance. The Hausman specification test was applied to select the most appropriate model, and relevant diagnostic tests are conducted to ensure the validity and reliability of the results. The study finding indicates that diversification has a mixed effect on financial performance. Income diversification, asset diversification, and investment diversification shows a positive and significant effect on ROA, while loan portfolio diversification shows a negative and significant effect on ROA. This suggests that although diversification generally enhances profitability, its effectiveness depends on the type of diversification and how it is managed. In conclusion, the study confirms that diversification is a key determinant of financial performance in Ethiopian private commercial banks, but its impact is not uniform across all dimensions. Based on the findings, it is recommended that banks should focus on expanding non-interest income sources, improving asset allocation efficiency, and strengthening investment strategies, while exercising caution in excessive loan portfolio diversification strategies.