Mariagerfjord is a municipality (Dens, kommune) in North Denmark Region in Denmark. It covers an aurie o 769 km² an a total population o 42,667 (2008).
On 1 Januar 2007 Mariagerfjord municipality wis creatit as the result o Kommunalreformen ("The Municipal Reform" o 2007), consistin o the umwhile municipalities o Arden, Hadsund an Hobro, an pairt o Mariager Municipality.
The municipality consists o the land aroond Mariager Fjord frae which the municipality takes its name.