The 2009–10 Tercera División was the fourth tier of football in Spain.
Play started on 29 August 2009 and ended on 20 June 2010 with the promotion play-off finals.
The following clubs finished as champions of their respective groups The 18 group champion clubs participated in the Group winners promotion play-off and the losers from these 9 play-off ties then proceeded to the Non-champions promotion play-off with clubs finishing second third and fourth.
Promoted to Segunda División B: Deportivo B, Gandía, Atlético Baleares, Alcalá, Real Sociedad B, Teruel, Badajoz, Caudal and Rayo B.
Promoted to Segunda División B: Getafe B, Yeclano, Coruxo, Santboià, La Muela, Alzira, Peña Sport, Extremadura and L'Hospitalet.