The 1991 Tercera División play-offs to Segunda División B from Tercera División (Promotion play-offs) were the final playoffs for the promotion from 1990–91 Tercera División to 1991–92 Segunda División B.
The champion of every group (excluding reserve teams) took part in the play-off.
The teams play a league of four teams, divided into 17 groups of 5 zones.
The champion of each group is promoted to Segunda División B.