This study investigates whether the voluntary disclosure of business group is related to affiliates’ voluntary disclosure. Specifically, we examine whether the voluntary disclosures of representative firms are associated with those of affiliates. Considering the influence of controlling shareholders on the decision-makings of affiliates such as income transfer or mergers between affiliated firms and the importance of voluntary disclosure in firm value, controlling shareholders are expected to affect voluntary disclosure decision-making of affiliates. The first hypothesis of this study examines the effect of controlling shareholders on voluntary disclosure of affiliates by using the association of voluntary disclosure between representative firm and affiliates. This association can be different depending on the private information of the business group because voluntary disclosure accompanies disclosure cost. Given that favorable information has lower disclosure cost, we expect that the association of voluntary disclosure between representative firms and affiliates is significant in the business group having favorable private information. We further examine whether the association between the voluntary disclosure of representative firms and that of affiliates is significant (insignificant) when they have same (different) private information. Our empirical analyses use 605 firm-year observations listed on Korean stock exchange market and belonging to large business groups over 2009 to 2012. We use the fair disclosure of a representative firm in a group as the group voluntary disclosure. To control the effect of no private information on voluntary disclosure, we use earnings related fair disclosure because all companies are expected to have private information associated with earnings. The empirical findings are summarized as follows. First, we find that the voluntary disclosures of representative firms are significantly associated with those of affiliates. Second, the association is significant when representative firms have favorable private information. Third, the association remains same when they both have same private information, but it is not significant when they have different private information. Our results suggest that controlling shareholders also affect the decision-making of voluntary disclosure, but affiliates selectively accept the voluntary disclosure strategy of the group considering its impact on their firms. In additional tests, we find that voluntary disclosure strategy of affiliates different from group disclosure policy also contributes to firm value, indicating the controlling shareholders’ effect with respect to voluntary disclosure. We believe our results help investors to understand the voluntary disclosure of the business group by identifying that the voluntary disclosure of the group is an important factor affecting that of affiliates. In addition to this, our results show that the homogeneity of private information plays a critical role in adopting the group voluntary disclosure policy.