The text of the treaty was prepared and initialled in Zagreb on 10 September and is based on the European Extradition Convention.
The ministers told a news conference in Podgorica that their respective countries aimed to develop cooperation in the struggle against organised crime.
"No criminal can be sure that he will avoid justice," the Croatian minister said.
Radovic said the treaty went into force today although it would be later ratified by the two parliaments.
The ministers declined to answer whether Croatia would ask Montenegro to hand over some of its citizens who were involved in military attacks on Dubrovnik in 1991 and 1992.
They said that the concrete names would be discussed later.