The study of polycentrism is responsible for identifying subcenters that integrate urban systems, as well as measuring the magnitude of the phenomenon in urban reality. This paper presents the analysis of measure of functional polycentricity, applying the functional polycentricity index presented by Green (2007) for seven metropolitan areas in Spain; finding their determinants, incorporating variables of magnitude, territorial balance and complexity to a linear regression model. It was found that from the functional perspective, the studied metropolitan areas of Spain have low levels of polycentricity. In order of magnitude was found to be less polycentric in their subsystems, Zaragoza, Madrid and Seville metropolitan areas; and in contrast Bilbao, Barcelona and Valencia with the largest. Malaga was found as a medium polycentricity level system despite the presence of few subcenters. Was found also that, although the incipient index, the variables that can best explain polycentricity are the size of the subsystem and number of nodes, the specialization and diversity of jobs, and also variables that explain income and mobility within municipalities of the subsystems that conform metropolitan areas in study.