The suspect was taken to the hospital for treatment of a gunshot wound and is "in stable condition," Eugene Police said.
Officials said both of the security guards with the Garda armored transport vehicle were unharmed.
Sgt. Ron Tinseth said officers were called out to reports of a shooting near 60 Division Ave. just after 3:40 p.m. Saturday.
Investigators say a man armed with pepper spray and a screwdriver tried to rob an armored car outside of the Albertson's store off of River Road.
One of the security guards fired three shots and hit the suspect, officials said.
One of the guards drove the armored truck across Division Ave. before calling law enforcement to make sure they were parked in a safe place, Eugene Police spokeswoman Melinda McLaughlin said.
Sgt. Tinseth said the suspect was taken to the hospital for treatment where he is listed "in stable condition."
One of the bullets went through the front window of the Albertson's store and was found embedded in a wall, witnesses said.