"Some of your opponents have said, 'Look, Donald Trump gave $100,000 to this Clinton Foundation.' And you say?" O'Reilly asked.
Trump portrayed himself as a businessman who would give to anybody to help his bottom line.
"Over the years I've been called a great businessman. They just said in one of the articles that I'm a world-class businessman," Trump said.
"I got along with Democrats and liberals and Republicans and conservatives," he added. "And they called me. And they loved me. And if they wanted to have dinner, they'd call me. And whatever I wanted, I got. I mean, that's part of being a successful businessman."
O'Reilly suggested that Trump's donations might not have been completely above board.
"So you bribed them?" the Fox host asked with a smile as he and Trump talked over one another. "You bribed them? As a businessman, you bribed them. You bribed them."
O'Reilly pointed out that one potential issue in the 2016 general election is the Clinton Foundation. Some Republicans have accused former Secretary of State Hillary Clinton, the Democratic front-runner, of trading government favors for contributions, though Clinton fiercely denies that suggestion.
"You gave $100,000 to the Clinton Foundation," O'Reilly said. "Now she's in trouble. ... So if you're the Republican nominee, how can you attack her on that when she'll turn around and say, 'You gave me $100,000 to do what I did.'"
Trump dismissed the idea that he'd have any trouble criticizing Clinton on the topic. He also said he thought the Clinton Foundation had less overhead at the time he contributed to it.
"It's very easy. It's very easy," Trump said. "And I'll have to tell you this: In all fairness, I thought that money was being put to very good use. I assumed it was being put to - whether it's Haiti, or all of the different things that I heard about - I didn't know about the private airplane rides all over the place."
Trump added: "I got along with everybody, Bill. I got along with everybody."
According to the Clinton Foundation's website, Trump gave between $100,001 and $250,000 to the nonprofit. Trump told O'Reilly that he would "love" to have his money back.