In this work microwaves were used as heating source to quantitatively evaluate the extension of damaged areas in composite materials using the thermographic technique. In particular, microwave pulsed thermography was carried out on CFRP damaged specimens. A new procedure was developed to process thermographic data obtained by microwave thermography tests and a new algorithm was used to processing thermography data. The approach used to evaluate the damaged areas is based on the characteristic non-linear heating behaviour and an higher slope of heating and cooling curves respect to undamaged area. The results obtained with new procedure were compared with other NDT techniques such as X-ray and lock-in thermography. Numerical simulations were carried out in order to assess the potential sensitivity of the new procedure. The aim of this work is to develop a quick procedure and data analysis in order to allow the non destructive testing of composite large structures in automatic way with a reduced testing time.