Sitiveni O. Mafi (born 9 December 1989) is a Tongan rugby union player. He plays in the lock and occasionally flanker position for the English Premiership Rugby side, London Irish. Mafi also represents Tonga at international level. Mafi previously played for the Leicester Tigers and New South Wales Waratahs. Mafi played as a replacement during the 2013 Premiership final as Leicester defeated Northampton Saints. In the final of the 2017–18 Top 14 season he scored a try after coming on as a replacement as Castres defeated Montpellier.