In the interview with PBS, to be aired on Monday, he also suggested his allies would retaliate if the West attacked.
US Secretary of State John Kerry has been lobbying hard for military action against Mr Assad during talks with EU and Arab foreign ministers in Europe.
Congress is due to debate whether to authorise intervention in Syria.
Lawmakers will return from their summer recess on Monday to start discussing President Barack Obama's resolution to launch a “limited, narrow” strike.
A Senate vote on the issue is expected as early as Wednesday, although the timetable for Mr Obama's request is less certain in the House, where the measure faces an even rockier time.
The US accuses Mr Assad's forces of killing 1,429 people in a sarin gas attack on 21 August on the outskirts of the capital, Damascus.
Mr Assad's government blames the attack on rebels fighting to overthrow him in the country's two-and-a-half-year civil war, which has claimed some 100,000 lives, according to UN estimates.
In his interview with PBS, the Syrian president said it was up to the US to prove that his forces were behind the Damascus attack.
“There has been no evidence that I used chemical weapons against my own people,” he told the network.
Mr Assad would neither confirm nor deny that his government kept chemical weapons, but said that if they existed, they were “in centralised control”.
Mr Assad also reportedly “suggested that there would be, among people that are aligned with him, some kind of retaliation if a strike was made”, PBS said.
Syria's allies include China and Russia, as well as Iran and the militant Hezbollah movement in Lebanon.
On a visit to Moscow, Syrian Foreign Minister Walid Muallem said the US was using the issue of chemical weapons as a “pretext” to launch a war.
Russian Foreign Minister Sergei Lavrov said there was no alternative to a peaceful solution to the crisis – and Moscow was convinced it was possible.
“We appeal to our American colleagues to concentrate on this [the Geneva conference] and not for preparing for a war scenario”.
Speaking in London shortly afterwards, US Secretary of State John Kerry agreed that the end of the conflict required a political solution but he warned that the “risk of not acting is greater than the risk of acting”.
“If one party believes that he can rub out countless numbers of his own citizens with impunity using chemical weapons… he will never come to a negotiating table.”
Responding to the latest remarks by President Assad, UK Foreign Secretary William Hague cautioned against believing what he said.
“We mustn't fall into the trap of attaching too much credibility to the words of a leader – President Assad – who has presided over so many war crimes and crimes against humanity,” Mr Hague said.
The White House has admitted it has no “irrefutable” evidence of Mr Assad's involvement in the August attack, but said a “strong common-sense test irrespective of the intelligence” suggested his government was responsible.
“We've seen the video proof of the outcome of those attacks,” White House Chief of Staff Dennis McDonough said on Sunday.
“Now do we have a picture or do we have irrefutable beyond-a-reasonable-doubt evidence? This is not a court of law and intelligence does not work that way.”
The British parliament has already voted against the UK joining any US-led military intervention in Syria.