The Nature Sanctuary “Serranía El Ciprés” is considered as a hotspot for the conservation of biodiversity at regional and national level in Chile. It is located administratively in the Valparaiso Region. in the Mediterranean eco-region. The objective of this work is to study the richness and composition of its vascular flora. The results indicate that there are at least 297 taxa in the area, belonging to 293 species, 183 genera and 74 families. The best represented families are Asteraceae, Fabaceae and Poaceae. The species richness in relation to the area is greater than expected in central Chile (226-272), where 272 (92.8%) are native, of which 145 (53.3%) are endemic to Chile and 21 (7.2%) are foreign. The predominant Raunkiaer life forms were hemicryptophytes (26.4%), terophytes (23.5%) and camephytes (17.7%). Ten species were officially classified in some categories of conservation, five of them as “vulnerable”, they are Citronella mucronata, Eriosyce aurata, Placea ornata, Porlieria chilensis and Prosopis chilensis. There are also seven new species for the Region.