Agios Konstantinos was a municipality in the prefecture of Phthiotida, which was established with the Kapodistrias plan in 1997. It was abolished in 2010 with the implementation of the Kallikratis plan and became part of the new municipality of Kamenon Vourla (tangible 2018). It was located in the south of the prefecture between the former municipalities of Atalanti and Dafnousia. It was one of the municipalities that make up the province of Lokrida. The municipality consisted of two municipal districts, occupying an area of 72.2 sq.km. and had a total population of 3,410 inhabitants. The seat of the municipality was Agios Konstantinos.