Objective: Propose an evaluation model of management quality of nongovernmental organizations (NGO), the so-called Third Sector, in the area social work and with municipal scope, based on the criteria of excellence utilized by the National Quality Prize (NQP). Context: The development of this masters` research takes place in the framework of the results of studies on the impact of non- governmental organizations activities which point out their evasiveness and inefficiency. The research aims to fill in this vulnerability and, therefore, improve the quality of the social intervention carried out by the NGOs in Brazil. Methodology: (i) Bibliographic research and analysis of management evaluation methods applicable to Third Sector organizations; (ii) study of the NQP, particularly its excellence criteria, which in the scope of the research were subdivided in items and for each an evaluation was made of levels of practice regarding management; (iii) construction of a proposal of a metric and a methodology for quality evaluation in non-governmental organizations incorporating criteria adapted from NQP and criteria coming out of the literature analysis and (iv) test in a NGO to validate the model. Conclusions: By employing metrics and validating them in accordance with metrological precepts, the study contributes to the measurement of quality in non-governmental organizations, thus collaborating to improvements in their performance through the overcoming of those fragile points identified in the processes of internal evaluation of their management.