Officers were dispatched to the Christiana Mall in Newark at 12:12 p.m. Wednesday.
According to investigators, two male shoplifters - ages 17 and 18 - were spotted by a security guard stealing clothes from Macy's and followed out of the mall.
They were fleeing on foot through the Macy's parking lot, police said, when one of them opened fire at the guard with a silver handgun.
"At one point he attempted to detain one of the suspects by putting his hand on his shoulder. That suspect then turned around and fired a single shot from a handgun at the security guard," said Cpl. Jeffrey Hale of the Delaware State Police.
The guard was not injured.
The suspects continued their escape through the parking lot, but police in the area spotted the suspects attempting to get on a DART bus and apprehended them at the bus on Old Baltimore Pike at Edgebrook Way.
Police say the gun used and the stolen clothes have been recovered.
The men arrested have not yet been identified.
The Christiana Mall issued a statement saying, "The safety and well-being of our shoppers, merchants and employees is of paramount importance."