The 1977–78 Segunda División B was the first season of Segunda División B, the third highest level of the Spanish football league system.
A total of 20 teams will contest the group, including 1 relegated from the Segunda División and 19 promoted from the Tercera División.
Teams relegated from 1976–77 Segunda División Teams promoted from 1976–77 Tercera División Teams from Aragon, Asturias, Basque Provinces, Galicia, León, Navarre, New Castile and Old Castile.
A total of 20 teams will contest the group, including 3 relegated from the Segunda División and 17 promoted from the Tercera División.
Teams relegated from 1976–77 Segunda División Teams promoted from 1976–77 Tercera División Teams from Andalusia, Balearic Islands, Catalonia, Extremadura and Valencia.