The blaze was reported at the Glen-Howard Plaza on the 600 block of Glenoaks Boulevard around 9:54 a.m. The strip mall includes a deli, a restaurant and a dry cleaners.
The fire may have started in the dry cleaning business and spread quickly, causing "significant damage to the entire mall," said Glendale police Sgt. Tom Lorenz.
After about 90 minutes, firefighters had nearly extinguished the fire, and were working to douse hot spots, Lorenz said.
Business owner Robert Minaeizadeh, who just bought Glenoaks Deli and Grocery last month, said he can't believe the loss.
"I just spent almost $80,000 for equipments," he said.
Firefighters were able to save a lot of the deli, but the roof was damaged.
The cause of the fire remains under investigation.
A senior citizen was treated by paramedics at the scene after suffering difficulty breathing, but no other injuries were reported.
City News Service contributed to this report.