Whittier police say they responded to the 11700 block of Telegraph Road near City Hall at about 1 a.m. and found the man's body.
The man, identified as Ricky Munoz, had traumatic head injuries and was pronounced dead at the scene, police said.
John Scoggins with Whittier police said it was not immediately clear if the man's death was the result of a traffic accident or if there was a "criminal element involved."
Telegraph Road was closed between Pioneer Boulevard and Alburtis Avenue as traffic and homicide detectives investigated.