Founded in 1923 as Club Deportivo Roca, the club started playing senior competitions three years later, and enjoyed their best years in the following decade, where they won six Segunda Regional de Guipúzcoa titles (but rejected promotion) and played in the 1935 Copa del Presidente de la República.[1] After the Spanish Civil War, the club began their association with Real Unión, having agreements of affiliation to act as their reserve team,[1] but ceased activities in 1970.
In 1980, Roca returned to an active status, but now under the name of Club Deportivo Roca-Real Unión, again as an affiliate side of the Txuri-beltz.[1] In 1992, after a change of ruling which obliged most of the reserve sides to adopt naming, shield and kits of their parent club, Roca was renamed Real Unión B.[1]
Real Unión B achieved a first-ever promotion to a national division in 2000, reaching the Tercera División.[1] Relegated in 2002, the club returned to the fourth tier in 2006, being immediately relegated back.[1]
