The shuttle lifted off from the Kennedy Space Center in Florida at 7:55 p.m. on Friday (00:55 GMT Saturday) and entered orbit nine minutes later. It is due to dock with the ISS on Sunday.
Endeavour will deliver equipment to enable the ISS to hold six crew members, instead of the current three.
The shuttle STS-126 mission, labeled "Extreme Home Improvements," will also see four spacewalks, including work on the station's solar power system.
The mission will see the crew install an additional bathroom, a refrigerator, a second toilet, and extra exercise equipment.
NASA intends to double the crew size of the ISS as early as May, 2009.
The shuttle's crew of seven includes U.S. astronaut Sandra Magnus, who will take the place of current ISS astronaut Greg Chamitoff. She will stay on the ISS until spring.
