Tvarditsa (Bulgarian: Твърдица [tvɐrˈdit͡sɐ]) is a town in Sliven Province, Southeastern Bulgaria.

It is the administrative centre of the homonymous Tvarditsa Municipality.

[2] The Bessarabian Bulgarian village of Tvardiţa in Taraclia District, Moldova, was founded by refugees from Tvardisa, who named it after their ancestral town.

Most inhabitants are ethnic Bulgarians (89%), followed by a large Romani minority (9%).

The main faith is Orthodox Christianity.