Sheriff Logan Marshall said USA Truck Stop on Georgia Highway 150, just a few miles east of Thomson, was robbed of an undisclosed amount of money shortly after 11 p.m. Tuesday night.
No one was injured during the robbery.
The robber was described as a black man and produced a handgun, the sheriff said.
On Monday night, a man armed with a handgun and who presented the clerk to fill up a plastic bag with cash, got away with robbing the Shell Food Mart at 1965 Washington Road near Thomson.
The robbery there happened shortly before 10 p.m.
"There are similarities to both robberies," Marshall said.
The robber is described as a black man, standing 5 feet, 9 inches tall and weighing between 200 and 210 pounds. In both cases, a handgun was the choice of weapon.
The sheriff said his office and agents with the Georgia Bureau of Investigation Region 7 Office in Thomson are seeking the public's help.
"We asking the public to help us solve these crimes," Marshall said.
Anyone with information that might help authorities is asked to contact the McDuffie County Sheriff's Office at 706-595-2145.
Marshall said business owners should use extra precaution.
"They need to keep only a minimum amount of cash on hand," the sheriff said.
Mike Ayers, special agent in-charge of the local GBI office, added, "Cooperate with him. Don't resist him."