The purpose of this study is to investigate the effectiveness of intra-group transactionsamong business groups, which has been an issue in recent years. Specifically, we analyzed thecharacteristics of intra-group transactions focusing on transactions between individual companiesin both large business groups and small and medium business groups. The results for all types of business groups are as follows. First, if the industry relationshipbetween a company belonging to the business groups and its counterparty is high, then theperformance of the company is high as well; thus, internal product transactions are efficientbetween vertically integrated affiliates. Second, the performance of a company belonging to thebusiness groups is significantly negatively affected if the counterparty is a non-listed companywith high large shareholder ownership as well if it falls into a focused industry (e.g., systemsintegration, construction, logistics or advertisement). The analysis shows that controllingshareholders use tunneling activities as a means of passing down their wealth or pursuing theirprivate gains through “unfair cross-subsidization practices.” It also shows the existence ofpropping activities in which companies help their affiliates in a relatively distressed financialsituation; however, the performance of a company was significantly negatively affected whenthe leverage rate of the business partners was high. We therefore conclude that a transactionwith affiliates having such characteristics is inefficient. The results by business group are as follows. In large business groups, transactions areinefficiently carried out because the performance of a company which is belonging to thebusiness groups is significantly negatively affected if the counterparty belongs to a focusedindustry or its leverage level is high. In small and medium business groups, transactions areefficiently conducted in vertically integrated industries with a high industry relationship. Onthe other hand, transactions are inefficiently carried out if the counterparty is a non-listedcompany with high large shareholder ownership or a high leverage ratio, as both negativelyaffect corporate performance. The results show that both efficient and inefficient aspects exist in the intra-group transactionsof business groups. Therefore, when policy-makers establish intra-group transaction policies,they must root out cases in which the policies are misused for the private benefit of controllingshareholders by specifically analyzing them according to the characteristics of affiliates, whilealso considering that intra-group transactions could be used efficiently.