It broke out in the roof space of a semi-detached property on the Upper Lisburn Road at 11.16am on Wednesday, before spreading next door.
Seven fire appliances, including an aerial ladder platform, were called to the scene and crews found a well-developed blaze when they arrived.
It took almost four hours to extinguish, with the incident coming to an end at 3.13pm.
Extensive damage was caused to both houses however there was no one inside either at the time, and there were no reports of injuries.
The road was closed for a time but has now been reopened.
The cause of the fire is under investigation.