"Blue Stone"; German: Blauenstein; Hungarian: Kékkő) is a town and municipality in the Veľký Krtíš District of the Banská Bystrica Region of southern Slovakia.

It is located on the Krupina Plain (Slovak: Krupinská planina) on the Krtíš and Riečka rivers.

In 1910 the settlement had a population of 1,347, consisting mostly of Slovak inhabitants, though a significant Hungarian minority lived in Modrý Kameň as well.

Modrý Kameň belonged to Nógrád (Novohrad) county until the end of World War I.

During World War II, an illegal antifascist communist organization operated in the settlement.