The men's parachutes collided and deflated some 300 to 400 feet in the air, sending the men plummeting to the ground, the Riverside County Sheriff's Department said.
Emergency workers tried to resuscitate the men but they were pronounced dead on the scene at 4 p.m.
The sheriff-coroner's office identified the men as Patrick James McGowan of Menifee and Christopher David Stasky of San Diego, both 42.
Scott Smith, western regional director of the U.S. Parachute Association, told the Riverside Press-Enterprise that McGowan had worked with Skydive Perris as an instructor for almost two decades and oversaw parachuting activities at the airport.
"He had over 17,000 jumps," Smith told the newspaper.
Smith said Stasky was helping McGowan train parachute instructors for the Canadian military.
Skydive Perris didn't return phone messages.
Federal and local officials are investigating the deaths.
--- Information from: The Press-Enterprise