In this work we describe an instrument based on the use of a factor analysis technique in order to measure the quality of education within a Postgraduate degree offered by a public Spanish university. We showed that the instrument has satisfactory psychometric properties (reliability and validity). Regarding the factorial solution, three main dimensions have been determined, namely: importance given to the subject; educational resources and knowledge of the subject (previous and posterior). It is important to remark that these three dimensions were consistently detected in all the factorial analyses performed (total sample and separate academic years). These three dimensions should be considered as fundamental when designing an instrument to evaluate educational quality. These findings may be taken as a basis for the design of future strategies for the evaluation of educational quality on other type of degrees within the higher education area.