The 1999–00 Argentine Primera B Nacional was the 14th season of second division professional of football in Argentina.
34 teams competed; the champion and runner-up were promoted to Argentine Primera División.
The winning team was declared champion and was automatically promoted to Primera División.
The teams that lost in semifinal joined into the Quarterfinals of the Second Promotion Playoff, and the team that lost in the final joined in the semifinal of the Second Promotion Playoff.
The best two teams of the overall standings that were not promoted (Quilmes and Almagro) played against the 18th and the 17th placed of the Relegation Table of 1999–2000 Primera División.