This paper aims to provide a network analysis of the relationships of shareholders in the Italian stock market for understanding the relevance of portfolio diversification in integrated ownership and firms control. The analysis combines both a complex network and an operational research approach. The former is used for statistical analyses on portfolio diversification. The latter estimates integrated ownership considering the paths on the network, and it emphasizes the difference between ownership and control. The dataset consists of nearly 300 companies traded on the Italian Stock Market. Data were retrieved through CONSOB and AIDA database, and they are adjourned at 2008. The dataset is completed with information on banks and insurance companies. Such data were retrieved through BANKSCOPE and ISIS databases.