Montana Highway 3 (MT 3) is a highway in central Montana extending north from Billings to Great Falls.

[2][3] At its southern end, MT 3 begins at I-90 in Billings and travels northwest 47 miles (76 km) to US 12 near Lavina – this is the only section of MT 3 that is not concurrent with a US highway.

MT 3 joins US 12 and travels 45 miles (72 km) west to Harlowton, where it leaves US 12 and joins US 191, and travels north for 39 miles (63 km) to Eddie's Corner (near Moore).

At Eddie's Corner, MT 3 turns west, leaving US 191 and joining the US 87 / MT 200 concurrency, and travels west 65 miles (105 km) to Armington where US 89 joins the highway.

The corridor is anchored by Interstate 25 and is part of the larger Ports-to-Plains Alliance.