The results of the Global Entrepreneurship Monitor (GEM) suggest that indicators of entrepreneurial environment in Croatia are not favourable. These indicators are prerequisites for entrepreneurial activity and competitiveness. In the GEM results for 2019 Croatia as a member of the EU had the lowest ranking for eight out of twelve observed factors, which describe entrepreneurial environment. Since in Croatia all macro factors of the business ecosystem which represent prerequisites for innovation, productivity and competitiveness, had unfavourable results, attention should be directed to the micro level of entrepreneurship, in addition to physical infrastructure and dynamics of the market. The measured above average rate of the Entrepreneurial Employee Activity (EEA) is a hidden and unused component of the entrepreneurial potential of Croatia. Since EEA refers to innovative activity aimed at development of new products/services or establishing new business units, it can be used to stimulate the necessary development of new products in corporate structures. This would in turn prompt innovation and competitiveness of Croatian economy. EEA stimulates growth and profitability of companies and allows for positive macroeconomic outcomes. It has proven to be particularly favourable for the economic growth and development of countries in transition. The aim of this thesis is to research impacts on EEA in order to stimulate it and in such a way contribute to innovation and sustainable competitiveness of Croatian economy. The interconnection of business ecosystems, organisational factors and EEA was analysed in a qualitative research using a sample of sixteen businesses, eight of which from IT industry and eight from processing industry. It was established that business ecosystems differ depending on the type of industry and that they shape organisational factors which influence the EEA features and intensity. The causal link between ecosystems and EEA, in which industry acts as a mediator, was researched in the quantitative research based on GEM methodology. Using a sample of enterprising employees of the observed IT and processing companies and GEM population, it has been confirmed that business ecosystem has an impact on features of EEA but not on its intensity. Based on the research results it is assumed that businesses can stimulate entrepreneurial activity of employees by creating a suitable organisational structure and culture and implementing a business policy adapted to the ecosystem. Based on this assumption, proposals for stimulating EEA on micro and macroeconomic level are presented. Cluster entrepreneurial activity allows for a diversification of innovative activity and creation of an innovative system which will increase the innovation capacity of Croatian economy. Interdependence effect among the components of ecosystem can transfer the innovative influence of micro factors onto the macro factors and contribute to the development of suitable policies and programmes that imply obligatory change of regulatory framework. The intention and research objectives as well as sources and data collection methods are described in the introduction of the thesis. In line with the set research objectives, the theoretical framework was set for the concept of entrepreneurship and entrepreneurial businesses. In order to explain the impact on EEA and its contribution to entrepreneurship, the model of Antocic and Hisrich and the GEM model were developed theoretically and conceptually as well as the concept of innovation and competitiveness on micro and macroeconomic level, followed by methodology used and research results. The discussion is followed by the detected research limitations. Based on the obtained results, taking into account the limitations of the conducted research, proposals for stimulating EEA and strategic management of innovative activity on the national level are presented, followed by the conclusion which encompasses all abovementioned components of the thesis.