Canadian Pacific Railway spokesman Andy Cummings says the trains were conducting yard operations east of Medicine Hat on Saturday when the collision occurred.
Cummings says four cars derailed but none were carrying hazardous commodities.
He says it wasn't a head-on collision, and that one of the trains made contact with the other 41 cars deep.
The Transportation Safety Board says it is sending a team to investigate.
Cummings says the conductor has since been released from hospital.
He couldn't immediately say what effect the interruption would have on the railway's operations, but noted that there was capacity to re-route trains around the area.