This study examined the effect of investment diversification on profitability of microfinance banks in Kenya. The specific objectives were to determine the effect of investment in Fixed deposits, investment in shares, investment in government securities and real estate investment on profitability of microfinance banks in Kenya. The study adopted a casual research design approach where the target population was based on 13 microfinance banks in Kenya. This study covered a 5-year period from 2017 to 2021. The study used secondary data that was extracted from the websites of the respective Microfinance banks. Both descriptive and inferential statistics were computed using STATA 15. Descriptive statistics included mean, standard deviation, Maximum and minimum. Inferential analysis included Pearson correlation and linear regression analyses. The study used panel regression analytical model. This study conducted serial correlation tests, heteroscedasticity tests and multicollinearity test to evaluate the data collected before the actual analysis. The findings revealed that investment diversification has positive effect on financial performance of microfinance banks in Kenya although there was mixed outcome in regards to significant effect. Investment in fixed deposits, real estate and shares were found to have significant effect whereas government securities was found to have insignificant positive effect. In this regard, the study concluded that investment diversification has positive effect on financial performance of microfinance banks in Kenya. The study therefore recommended management of microfinance banks microfinance banks should compare each of the fixed deposit options basing on desired risk, interest rate, and tenure, and choose a fixed deposit only after weighing the benefits and drawbacks of various fixed deposits on the market. High liquidity produced by microfinance banks' client deposits should be invested in a variety of government securities and bonds, which are backed by the government, the study suggested. The study recommended that microfinance banks can buy short-term Treasury bills directly or through a bank or broker.