This paper deals with the assessment of the thermal stress distribution in a composite/aluminium bonded joint. An aluminum specimen symmetrically reinforced with two composite patches is heated while both thermal and displacement fields are measured with an infrared camera and a CCD camera, respectively. The grid method is used to obtain the displacement fields in the composite patch. This displacement field is in good agreement with theoretical expectations. This enables us to deduce the longitudinal strain in the composite patch by fitting the displacement field with a suitable model and differentiating it. The shear stress peak which takes place in the adhesive near the free edge of the patch is finally estimated.