A car loaded with explosives targeted two buses transporting about 100 Egyptian soldiers to Cairo from el-Arish in northern Sinai, the Ma'an news agency said.
The Arabic language al-Ahram said 12 soldiers were killed and 35 injured by a car bomb that exploded as the buses went by.
Immediately following the bombing soldiers sealed off the area and began searching for the perpetrators, believed to be linked to al-Qaida affiliated groups operating in northern Sinai, the report said.
A security official described the bombing as one of the most deadly attacks in the Sinai Peninsula since President Mohamed Morsi was deposed in July.
In September the Egyptian army began a military campaign in the Sinai to crack down on militant groups conducting attacks on soldiers and civilians.