|Middle Branch Union River|
|East Branch Union River|
|195 feet (59 m)|
|Length||14 miles (23 km)|
|Progression||E. Br. Union R. – Graham Lake – Union River – Union River Bay|
The Middle Branch Union River is a river in Hancock County, Maine, United States. From the outflow of Lower Middle Branch Pond () in Aurora, the river runs 13.8 miles (22.2 km) west and south to its confluence with the East Branch of the Union River in Osborn.