Castro de Fuentidueña is a municipality in the province of Segovia, in the autonomous community of Castile and León, Spain. It is located in the central part of the country, within the Duero basin region of the Iberian Peninsula.
The municipality is small and sparsely populated. According to the 2004 census conducted by Spain's National Statistics Institute (INE), Castro de Fuentidueña had a population of 73 inhabitants. The name "Castro" derives from the Latin castrum, referring to a fortified settlement, a common element in place names across the Iberian Peninsula.
Like many rural municipalities in the province of Segovia, Castro de Fuentidueña is characterized by its small size and low population density, typical of the depopulated areas of inland Castile and León.