As an amateur boxer, Constantin Onofrei won the Romanian National Amateur Boxing Championship at the
super heavyweight division in 1995 and represented
Romania at the
men's super heavyweight event from the
2000 Summer Olympics where he lost in the first round at points against
Samuel Peter. He made his professional debut in 2001 at the age of 25 when he defeated Peter Simko by
knockout in the first round of a bout held at
Kisstadion from
Budapest. He won the German International
heavyweight title in 2002 after knocking-out
Roman Bugaj in the third round. Onofrei defended the German International heavyweight title twice by defeating Adnan Serin and Goran Gogic but lost it against
Taras Bidenko in a fight which was also for the
WBO Intercontinental heavyweight title. Onofrei's last match took place in 2007 when he lost by knockout against
Timo Hoffmann in the fourth round of a bout held in Stadhalle from
Rostock. ==Professional boxing record==