The 2005–06 Argentine Primera B Nacional was the 20th season of second division professional of football in Argentina.
A total of 20 teams competed; the champion and runner-up were promoted to Argentine Primera División.
The winning team played the Promotion Playoff Primera División-Primera B Nacional.
The Second Promotion playoff loser (Belgrano) and the Torneo Reducido Winner (Huracán) played against the 18th and the 17th placed of the Relegation Table of 2005–06 Primera División.
Note: Clubs with indirect affiliation with AFA are relegated to the Torneo Argentino A, while clubs directly affiliated face relegation to Primera B Metropolitana.