Media reports say the spokesman was accused of sexual abuse.
The presidential Blue House said Friday on its website that unspecified actions by Yoon Chang-jung marred the government's dignity.
It didn't elaborate. But South Korea's Yonhap news agency cites a Washington police complaint that says Yoon grabbed a Korean-American intern's buttocks on the night of the summit between Park and US President Barack Obama.
An email seeking police confirmation wasn't immediately answered. Yoon couldn't be reached for comment.
Yoon was a conservative columnist before joining Park's team last year. He became spokesman after her February inauguration.