The company says the locomotive slid off the track when it went over a broken rail along Front Street around 3:30 a.m.
It says the train wasn't going very fast and didn't tip over, nor did the 20 rail cars behind it.
Crews spent several hours getting the train back on track and as a result Front Street was entirely closed to traffic.
Southern Railway is a major freight transporter in the Lower Mainland and Fraser Valley, serving shippers of automobile, forest, building, agricultural, chemical and steel products.
No one was hurt in the incident.
(The Canadian Press/News1130)