This study examines the accounting choices using advertising expenditures to investigate controlling shareholders' opportunistic behavior in the perspective of related party transactions. We empirically analyze the relationship between an existence of related advertising company (Inhouse Agency) and advertising expenditures of conglomerates' subsidiaries. Furthermore, we investigate the impacts of controlling shareholders' ownership for Inhouse Agency on advertising expenditures of their related companies. The main regression models to examine hypotheses of this study are briefly described below in equations (1) and (2). ADVi,t = β0 + β1InhouseAgencyi,t + β2ADVi,t-1 + β3SIZEi,t+ β4ROAi,t-1 + β5LEVi,t + β6GROWi,t + β7CFOi,t+ β8TRi,t+ β9YD + β10IND + εi,t (1) Here, ADV represents advertising expenses, InhouseAgency dummy variable to represent an existence of related advertising company, SIZE natural log of total assets, ROA net income, LEV total liabilities, GROW sales growth, CFO cash flows from operations, TR education and training expenses, YD year dummy, IND industry dummy. ADV, CFO, TR are standardized by sales, ROA, LEV are standardized by total assets respectively for the control of heteroscedasticity. ADVi,t = β0 + β1Ownershipi,t + β2ADVi,t-1 + β3SIZEi,t+ β4ROAi,t-1 + β5LEVi,t + β6GROWi,t+ β7CFOi,t+ β8TRi,t+ β9YD + β10IND + εi,t (2) Here, Ownership represents controlling shareholders' cash flow rights for Inhouse Agency. We find that advertising expenses of the firms with Inhouse Agency are significantly higher than those of the firms without Inhouse Agency even after controlling for prior advertising expenses level. This result indicates that an Inhouse Agency as a related party in Korean Chabol would be an important factor that influences firms' advertising expenditures. The second finding of this study is that advertising expenses of the firms with Inhouse Agency are affected by the cash flow rights of controlling shareholders' for the Inhouse Agency. The empirical result for analysis to examine the second hypothesis of this study shows that the firms with higher cash flow rights of the controlling shareholders' for Inhouse Agency increase advertising expenditures after controlling firm's size, return on assets, leverage ratio, sales growth, cash flows from operations and training expenses. These results provide implications on making the strategic decision to regulatory agencies like Fair Trade Commission because they are currently focusing on related party transactions of conglomerates with controlling shareholder. Futhermore, the empirical results of this study are expected to help the external auditors for auditing firms' abnormal advertising expenses and external investors when they make investing decisions particularly in terms of the related party transactions with advertising expenditures influenced by the pursuit of controlling shareholders' private benefits probably.