Thermally-induced failure is a major reliability issue for electronic packaging. Due to highly nonlinearity of packaging materials, the electronic packages exhibit uneven thermal deformation in the whole temperature range during thermal cycling. This behavior will affect the buildup of thermal strain and thermal stress within packages, which may affect the reliability of the packaging. Therefore, a real time method is needed to monitor the thermal deformation of packages during the thermal cycling. In this study, the real time moiré interferometry technique is used to monitor the thermal deformation of a plastic package. A grating is transferred onto the cross section of the sample at room temperature. Then the sample is placed in a thermal vacuum chamber and the temperature is increased from room temperature to high temperature. A moiré interferometry setup is used to monitor the thermal deformation of the package with the increase of temperature. The fringe patterns are recorded by a CCD camera system and are compared with the displacement contours of nonlinear finite element simulations. The results show that the real time moiré interferometry technique is an effective way to monitor the thermal deformation of electronic packaging and also provide a powerful validation method for finite element analysis. The comparison between the moiré fringe patterns and finite element results also shows a good agreement.