This research investigates the diversification-performance relationship in Nigerian banking industry. Empirical evidences emerging from previous studies from developed countries about the effect of diversification on performance in the banking industry have so far yielded mixed results. There is a major gap in the relevant literature on developing countries which this research filled by studying Nigerian banks and providing empirical evidence on diversification-performance relationship. Survey research design was adopted with the application of probability sampling technique in selecting our case study companies and respondents. Primary data were collected through questionnaire while secondary data were garnered from the annual report and accounts of the banks under study. Data were analyzed through descriptive statistics while correlation and ANOVA were used to test our hypotheses. It was discovered that diversification impacts corporate performance of these banks positively and recommends that these banks should engage in geographical diversification in addition to other forms of diversification they are currently involved in for maximum performance.