He had his first cap for Romania, at 20 February 2000, in a 39–10 win over the Netherlands. He was selected for the 2003 Rugby World Cup finals, playing all the four matches and scoring a try, and for the 2007 Rugby World Cup finals, playing again in all the four matches.
Sîrbu had 76 caps, from 1996 to 2011, with 9 tries scored, 45 points in aggregate.