The former technology executive cited concerns about terrorism in explaining her position during an appearance on CBS' "Face the Nation" that the US "sadly, cannot relax our entrance criteria."
An estimated 4 million refugees have fled Syria since 2011. The United States has accepted about 1,000 Syrians this year among 70,000 refugees from across the world.
Some have called on the US to expand its refugee program. Gen Martin Dempsey, chairman of the Joint Chiefs of Staff, described the situation as "a shared responsibility among the civilised nation states of the world," in an interview that aired today on ABC's "This Week."
Fiorina remains a long-shot to win the Republican nomination, although polls show she has risen to the middle of the pack of 17 candidates since making a strong performance in the first Republican presidential debate.
Ohio Governor John Kasich, another Republican presidential candidate, suggested there was room for the United States to play a bigger role.
"I think we do have a responsibility in terms of taking some more folks in making sure they assimilate, and at the same time, helping people to actually be safe as they move that's logistical support," he told ABC. "But this is fundamentally an issue that Europe has to come to grips with.