The 2009–10 National League 2 South was the first season (23rd overall) of the fourth tier (south) of the English domestic rugby union competitions since the professionalised format of the second division was introduced. Previously known as National Division 3 South, it had been renamed due to widespread changes to the league system by the RFU with National One becoming the Championship, National 2 becoming National 1 and so on. The league system was 4 points for a win, 2 points for a draw and additional bonus points being awarded for scoring 4 or more tries and/or losing within 7 points of the victorious team. In terms of promotion the league champions would go straight up into National League 1 while the runners up would have a one-game playoff against the runners up from National League