The season 2003–04 of Segunda División B of Spanish football started August 2003 and ended May 2004.
Playoffs de Ascenso: Relegated from Segunda División: Promoted from Tercera División: Relegated: Administrative relegation: Occupied the vacant spots by administrative relegations: Teams from Asturias, Basque Country, Cantabria, Galicia, La Rioja and Navarre.
Teams from Aragon, Castilla–La Mancha, Castile and León, Community of Madrid and Galicia.
Teams from Balearic Islands, Catalonia, Region of Murcia and Valencian Community.
Teams from Andalucia, Canary Islands, Ceuta, Extremadura and Melilla.