The advancement of innovative technologies such as artificial intelligence (AI) and big data has considerably increased in the amount of financial data. However, the quantity of abnormal data belonging to minority classes is relatively low, resulting in an exacerbation of data imbalance phenomenon. Data imbalance significantly impairs the performance of classifiers for minority classes. In this study, classification performance comparison experiments were conducted according to the data imbalance resolution methodology using credit card customer data, one of the financial data. Empirical analysis revealed that as the degree of data imbalance decreased, the performance of the classification model tended to improve, and applying the data imbalance resolution methodology led to performance enhancement. When SMOTETomek was applied, the deep neural network (DNN) showed the highest performance improvement, and the performance of the classification model could be improved using a conditional adversarial generative network (CGAN) for financial data. This study proposed solutions for data imbalance that could be applied to financial data, and the proposed methods contributed to the adoption and development of AI technology in the financial industry by making it more suitable for financial practices.