| Province: | QC |
| Type: | QC |
| Route: | 125 |
| Maint: | Transports Québec |
| Map: | Route 125-QC.png |
| Length Km: | 132.6 |
| Length Round: | 1 |
| Direction B: | North |
| Direction A: | South |
| Terminus A: | in Montréal |
| Terminus B: | Mont-Tremblant National Park in Saint-Donat |
| Junction: | in Montréal in Laval in Laval and Terrebonne in Saint-Esprit |
| Previous Type: | QC |
| Previous Route: | 122 |
| Next Type: | QC |
| Next Route: | 131 |
Route 125 is a Quebec highway running from Montreal (on Pie-IX Boulevard near the Olympic Stadium) to Saint-Donat, Lanaudière, Quebec in the Lanaudière. The southern section of Route 125 runs parallel to Autoroute 25 in Laval, Mascouche, and Terrebonne. At Saint-Esprit, the Autoroute ends, and 125 continues northwards until the entrance to the Mont Tremblant Provincial Park north of Saint-Donat.
Route 125, a road parallel to the A-25, begins at the corner of Sherbrooke Street East (Route 138) in Montréal, under the name of "Boulevard Pie-IX." It keeps this name until it meets with the A-440 after crossing the Rivière des Prairies on the Pie-IX Bridge. In between the Pie-IX Bridge and the A-440, it has a highway configuration and has two lanes in each direction separated by a median, crossing the streets it crosses with the help of an overpass and connected to these lanes by access ramps.
It then crosses the Île Jésus (Laval) and the Mille Îles River on the Sophie-Masson Bridge to arrive in Terrebonne. Following its concurrency with the A-440, it looks more like a secondary road, being quite narrow until Route 344, with which it makes a small concurrency before joining the Montée Masson in Terrebonne. From there, it heads to the city of Mascouche, of which it is its main road. Once past the city of Mascouche, it looks again like a narrow secondary road and does not even have a double yellow line.
When it reaches Saint-Roch-de-l'Achigan, it is a little used country road. At the junction of Route 339, it takes it to form a small concurrency with the A-25 at its northern end. From Saint-Esprit, Route 125 becomes the main traffic route to the northwest of the Lanaudière region, the A-25 ending at Saint-Esprit. It heads towards Sainte-Julienne, where it forms a small concurrency with Route 337 to the vicinity of Rawdon.
After Chertsey, for about 10 kilometres in the Entrelacs sector, it is a four-lane divided road. It then reaches Saint-Donat before ending at the entrance of Mont-Tremblant National Park.