The 1945–46 Tercera División was the tenth edition of the Spanish third national tier.
The division comprised 100 clubs in 10 geographic groups.
The top 3 clubs in each group (30 in total) progressed to the Second Phase.
The 5 group winners progressed to the Final Phase - a group of 5 clubs, each playing 8 matches.
Note: Baracaldo were promoted to the Segunda División.