The article presents corporate models of enterprise and from that models derives managers motivation to merge enterprises. It analyses the influence of motivation on enterprise's economic effectiveness. The analyses of theoretical models proves that the enterprises' growth based on the motive of maximum utility for the managers may be profitable but the growth In itself is not necessary or sufficient to improve enterprise's effectiveness. Foreign research do not prove whether fusions and mergers are beneficial for the enterprises. Therefore presented relations should be analysed in further research.