This paper investigates the effect of conglomerate diversification on company performance. Using industrial diversification and international conglomerates, this studies examines the moderating effect of managerial ownership on the relationship between conglomerate diversification and the performance of family businesses that have managerial ownership and listed on the Indonesia Stock Exchange from 2010-2016. Using two proxies of performance, including accounting-based performance (ROA) and market-based performance (MBV). The empirical result indicates that industrial diversification show positive and significant relationship with performance (ROA and MBV), while international conglomeration show negative and significant relationship with performance (ROA and MBV). Further, managerial ownership has no moderating effect on a MBV of a diversified companies. Regarding ROA, result show that managerial ownership has no significant effect on international diversification, however, for industrial diversification degrade ROA significantly. Mainwhile, using level of managerial ownership, the result show that level of managerial ownership no moderating effect on a performance, except that under lower managerial ownership, industrial diversification enchances ROA significantly, however, for international conglomerates degrade ROA significantly.