The 2005–06 National Division Three South was the sixth season (19th overall) of the fourth division (south) of the English domestic rugby union competition using the name National Division Three South. New teams to the division included Bracknell and Rosslyn Park who were relegated from 2004–05 National Division Two while Cambridge came up as champions of London Division 1 along with Cinderford (champions) and Bridgwater & Albion (playoffs) who were promoted from South West Division 1. 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 Division Two while the runners up would have