The motivation for the Author’s own research on the district-commune co-opetition as a factor of common territorial competitiveness stems from several reasons. The first refers to the fact that so far, such topics as the subject of this article have not been discussed in the source literature. The second reason is related to the fact that the competitiveness of local governments affects the quality of life of their residents, which is becoming increasingly important today. Therefore, such research seems to be original and important. The third reason arises directly from the scientific interests of the Author who has been the mayor of a Polish urban-rural municipality for 20 years (1998-2018) and is currently the councillor of the Mazovian parliament. In the research project the triangulation method was applied. It was based on quantitative (CSO data, local government budgets) and qualitative research (Author’s participant observation, opinions of the district governor and the mayor, in-depth interviews). As a result of the research conducted it was established that district-municipal co-opetition could help to increase competitiveness of common local territory in the district and municipality and other municipalities. There were identified detailed determinants and different forms of this coopetition: financial, property, intercommunal social capital. Co-opetition between county and municipalities, as a non-obligatory relationship between self-governments, should be developed even more voluntarily in the form of in-depth partnership, because the county and municipalities benefit from the improved competitiveness through the multiplication of social capital, financial and property resources. This has a significant impact on improving the quality of life of the inhabitants in the common local territory.