Mario Klabin Xavier Romancini (born December 15, 1987, in Telêmaco Borba[1]) is a professional racing driver from Brazil.

After his impressive debut season, Romancini moved up to the South American Formula Three championship in 2007 with leading team Cesário F3.

During the season he took ten podium places in fourteen races, including two wins, to finish runner-up in the championship behind team-mate Clemente de Faria, Jr.In November 2007, Romancini took part in World Series by Renault testing at both Paul Ricard and Valencia, driving for Epsilon Euskadi, Prema Powerteam and the reigning champions Tech 1 Racing.

In January 2008 he was signed by Epsilon Euskadi to partner Frenchman and fellow rookie Alexandre Marsoin.

[2] During the season, he scored two points finishes and was lying 28th in the standings when he left the team due to sponsorship problems with two rounds of the championship remaining.