Purpose: Study impact of business activities on selection of sources of enterprises' competitive advantage. The research hypothesis is advanced as H1: scope of business objects (sector) is a factor differentiating selection of sources of competitive advantage by enterprises. The concept and essence of competitiveness are discussed, methods of building competitive advantage by enterprises are detailed. Design/Methodology/Approach: The theoretical section follows a comprehensive review of leading specialist literature. The hypothesis is verified in the empirical section by means of position measures (arithmetic mean, median) and variability measures (standard deviation, coefficient of variability). Kruskal-Wallis test is also used to verify the research hypothesis. Findings: The paper contains results of a survey of 253 large Polish enterprises. Kruskal-Wallis test serves to determine impact of a sector on selection of sources of enterprise competitive advantage. Sector has no effect on choice of such sources as: quality management system, cost reduction, advertising, public relations, enterprise image, highly qualified managerial staff, knowledge and skills of employees, new technologies, or customer trust. Practical Implications: The results can be utilised by enterprises as guidelines for selection of sources of competitive advantage. Originality/Value: The paper contains an original study of a representative group of large enterprises that can be generalised to the whole population assuming a confidence level α=95% and maximum error β=6%.