The purpose of this research is to find the impact of diversification strategy of a firm to the firm’s financial performance with proportion of independent board of commissioners as the moderating variable in manufacturing firm listed on Indonesia Stock Exchange (ISE) for the period of 2013-2015. Independent variable for this research is diversification strategy which is being measured using Hierschman Herfindahl Index (HHI). Moderating variable for this research is proportion of independent board of commissioners which is being measured using board of commissioners’ ratio (PDKI). Dependent variable for this research is firm’s financial performance which is being measured using Return on Assets (ROA). There are 113 observational data that is used as the sample for this research. This research is conducted by IBM SPSS Statistics 23.0 using multiple linear regression analysis with 5% significance. The result of this research indicates that HHI has a positive but not significance influences towards ROA. HHI which is moderated by PDKI has a significance but negative influences towards ROA |