The air tanker was dropping retardant on the 5,000-acre White Rock Fire when it went down in the Hamblin Valley area of western Utah, Bureau of Land Management officials said.
When the plane went down, the tanker was on its second run of the day.
Crews held the fire back from the wreckage, as sheriff's deputies drove and hiked for more than an hour to reach the site and confirm that the pilots had died. The victims were identified as Todd Neal Tompkins and Ronnie Edwin Chambless, both of Boise, Idaho.
The pilots were flying a P-2V air tanker that is owned by Neptune Aviation Services of Missoula, Mont. The cause of the crash is unknown at this time.
The White Rock Fire began burning Friday night after a lightning strike in eastern Nevada. It spread across the Utah line Saturday night, but most of the blaze remained in Nevada.
Sunday's crash come several months after a group of Western senators questioned whether the Forest Service was moving quickly enough to build up and replace the fleet of aging planes that drop fire retardant on wildfires.
The Associated Press contributed to this report.
