The Nm23 gene is a metastatic suppressor identified in a melanoma cell line and expressed in different tumorswhere their levels of expression are associated with reduced or increased metastatic potential. Nm23 is one ofthe over 20 metastasis suppressor genes (MSGs) confirmed in vivo. It is highly conserved from yeast to human,implying a critical developmental function. Tumors with alteration of the p53 gene and reduced expression ofthe Nm23 gene are more prone to metastasis. Nm23-H1 has 3’-5’ exonuclease activity. This review focuses onthe role of Nm23 in cancer progression and also a potential novel target for cancer therapy.