The Sajó (-Hungarian; Slovak: Slaná) is a river in Slovakia and Hungary.
Its length is 229 km, of which 110 km is in Slovakia. Its source is in the Stolica Mountains range of the Slovak Ore Mountains. It flows through the Slovak town Rožňava and the Hungarian city Miskolc. In Hungary it flows through the county of Borsod-Abaúj-Zemplén. It flows into the River Tisza near Tiszaújváros.