Are There Important Differences in Success and in Organizational Culture between Family Companies in Production and Service Sector in Slovenia? In this article we will introduce the development of those organizational culture elements, which influence importantly on company successfulness in family companies. The research was performed in 24 Slovenian companies with 524 responded survey questionnaires from field of services, consultancy and computer equipment, trade counter, production, road freight traffic and civil engineering. With this analysis we found out the answer to the question in family loyalty to the company, management style, loyalty and mutual trust system, strategic emphasis, criteria for successful business operations, stimulation (rewarding), process of continuous improvement, business ethics of the company, organization, values of the employees, and satisfaction of the employees in those companies. The collected data are important from the aspect of the organizational culture influence on the future growth or eventually their stagnation.