For the leasing of real estate to be an economic activity, it is sufficient to have a full-time employee who manages the activity 

The Supreme Court has put an end to a traditional debate in the field of the benefits of the family business regime in the inheritance and gift tax, by ruling that (contrary to what the Administration and some courts had been arguing), no additional requirements can be demanded beyond those established by the Personal Income […]

El arrendamiento es actividad económica aunque su gestión se externalice, según confirma la Dirección General de Tributos

Real Estate leasing is an economic activity even when management is outsourced, according to the Directorate General of Taxes

According to the most recent criterion of the Directorate General of Taxes (DGT), real estate leasing can be classified as an economic activity for Corporate Income Tax purposes when managed by specialized experts who have been subcontracted, even if there is not a full-time employee exclusively dedicated to its management, as literally required by law. […]