| State: | ME |
| Type: | ME |
| Route: | 138 |
| Map Custom: | yes |
| Length Mi: | 9.48 |
| Length Round: | 2 |
| Length Ref: | [1] |
| Direction A: | South |
| Terminus A: | in Bowdoin |
| Junction: |
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| Direction B: | North |
| Terminus B: | in Richmond |
| Counties: | Sagadahoc |
| Next Type: | ME |
| Next Route: | 139 |
| Previous Type: | ME |
| Previous Route: | 137 |
State Route 138 (SR 138) is part of Maine's system of numbered state highways, located entirely in Sagadahoc County. It runs from U.S. Route 201 (US 201) in Bowdoin, to Interstate 295 (I-295) while running concurrent with SR 125 for 1miles. It then reaches SR 197 in Richmond, and ends at the junction with US 201 in Richmond.
SR 138 begins at an intersection with US 201 in Bowdoin. It heads east towards I-295, and SR 125 in Bowdoinham, where the two state routes run concurrent for 1miles. After splitting from SR 125 in Bowdoinham, SR 138 heads north through Richmond, where it intersects SR 197 and terminates at US 201 in Richmond.