In the past twenty years, research on the measurement of social capital has been among the leading areas of interest in social sciences. The impact of ethnic diversity on the level of social capital is an interesting aspect of this research. According to Robert Putnam, in the U.S. context, ethnic diversity has a negative influence on the level of social capital. Various research initiatives implemented in Europe indicate, however, that ethnic diversity does not have a significantly negative correlation with social capital, and, that examples of its positive impact on social capital can be found. The article presents a quantitative analysis conducted in 20 municipalities of the Opolskie Voivodship (10 of them ethnically homogeneous, and 10 – ethnically diversified) in order to analyse this relationship. On the basis of the data collected in the analysis, it can be stated that in the surveyed region, ethnic diversity is not a factor with a negative impact on the level of social capital, and it is also highly probable that it is a factor that enhances social capital, at least its bonding dimension.