Prince Turki al-Faisal told the BBC the action would have a negative impact, further entrenching Iran, Russia and the rule of President Bashar al-Assad.
US President Donald Trump announced in December that it was time to bring US troops home from Syria.
Prince Turki was speaking just before US Secretary of State Mike Pompeo began a visit to Riyadh.
Mr Pompeo is on a tour of the Middle East, and has already visited Iraq, Jordan, Egypt and Bahrain.
What did Prince Faisal say?
He said that the world community was guilty of neglecting the Syrian people and the US troop withdrawal would make things worse.
“The US actions from my perspective is that it is going to further complicate, rather find any solutions to it and further entrench not only the Iranians, but also the Russians and Bashar al Assad, so from the perspective it…