The Municipality of Kostanjevica na Krki (pronounced [kɔˈstaːnjɛʋitsa na ˈkəɾki] ⓘ; Slovene: Občina Kostanjevica na Krki) is a municipality in the traditional Lower Carniola region of southern Slovenia.

The seat of the municipality is the town of Kostanjevica na Krki.

It is part of the Lower Sava Statistical Region.

[2] It is located in the northern foothills of the Gorjanci Mountains and extends to the border with Croatia.

In addition to the municipal seat of Kostanjevica na Krki, the municipality also includes the following settlements: