This paper investigates the relative efficiency of public (state) libraries of major cities in Turkey by applying a data envelopment analysis. Scale, technical, and overall efficiency scores are calculated. It is found that there is a negative correlation between economic and social development index of the cities and efficiency scores of state libraries of same cities. In order to understand the sources of technical inefficiencies, the slack analysis is employed. Book collection and library staff are turned out to be the most problematic inputs and library members and lending of the books the most problematic outputs.