Sanu signed a contract with the Dolphins on Tuesday, Adam Schefter of ESPN reports.
Sanu turns 33 in August and hasn't reached 200 yards in a season since 2019. He was a functional third receiver for the 49ers before dealing with a knee injury last season, but he'll likely be lower on the depth chart in Miami so long as Tyreek Hill, Jaylen Waddle and Cedrick Wilson stay healthy.