Today in all developed countries around the world, great attention is given to service activities. The economies increasingly rely on them and the future growth is based on service improvement, research and development. In the Republic of Croatia, the number of employees is higher in services than in manufacturing and have a significant contribution to GDP. The former economy driving forces were manufacturing enterprises which today can not achieve a competitive advantage without supporting service activities. Service activities are subject to numerous researches and scientific analyzes and despite the already great presence, still represent a mystery and are a reason for constant study of their complexity. Services are a very complex area because of the specific characteristics that the products do not have. They are intangible, we can not store them and postpone consumption, and the perception of their quality is subjective and depends on the person who performs it. Services can be divided into many different types, and the most complicated one is the professional service, which requires far more effort in planning and performance than other types of services. Activities and operations are implemented in a different way and mass service operations management can not be applied here. Searching for the literature revealed a gap in the field of mass and professional service research. This two service types must be constantly explored in order to survive great and aggressive competition they are exposed to. The main aim of this paper was to identify the differences between professional and mass service in order to determine the diversity of operational practices in these two types of service companies and to give guidance to managers which practices to implement depending on which type of service company they manage. For this purpose, a survey was conducted using a questionnaire in ten companies of which five are mass-service companies, and five are professional. Results collected in the research confirmed the findings of the previous researches that differences between operations management of professional and mass services exist.