Rafael Hui Si-yan (born 8 February 1948) is a former Chief Secretary for Administration of Hong Kong and career civil servant.

On 19 December 2014, he was convicted and sentenced to imprisonment for misconduct in public office and bribery, and stripped of his honours and titles in March 2018.

In June 2000, he resigned from the civil service and he assumed the post of managing director of the Mandatory Provident Fund Schemes Authority.

Hui also served as the Vice-chairman of the Hong Kong Arts Festival Society and Chairman of its Programme Committee from 2001.

After retiring from the Chief Secretary for Administration, he served on the Executive Council of Hong Kong as an unofficial member from 2007 to 2009.