The 1965–66 Southern Football League season was the 63rd in the history of the league, an English football competition.
Weymouth won the championship for the second time in a row, whilst Barnet, Bath City, Burton Albion and Hillingdon Borough were all promoted to the Premier Division.
Nine Southern League clubs applied to join the Football League at the end of the season, but none were successful.
The Premier Division consisted of 22 clubs, including 18 clubs from the previous season and four new clubs, promoted from Division One:
Alongside the four League clubs facing re-election, a total of 14 non-League clubs applied for election, including nine Southern League clubs.