This paper examines the factors that affect the annual growth of cooperatives and investor owned firms (IOF) in Greek diary industry over the period 1990–94. A comparison based on both cooperative principals and property rights theory is made between IOFs and cooperatives to study their characteristics. However an empirical work is required to explain differences, if any, in the growth of the two types of firms within the same market. The work examines the determinants of the annual growth and it tests whether significant differences between IOFs and cooperatives exist. Ordinary least squares results show that both diversification and advertising strategies are important determinants for IOF growth, while the cooperative growth depends on capital structure and intensity and these organizations do not effectively apply competitive strategies.