The launch of the SPOT 4 satellite in March 1998, has given the opportunity to probe a Modulation Transfer Function (MTF) measurement method relying on bi-resolution images and to perform an in-flight MTF assessment for VEGETATION, a wide field of view sensor. The following paper begins with a presentation of the theoretical basis of the method, putting the stress on the sampling and windowing aspects and on the implicit requirements over the data for this method. The next step gives an overview of the SPOT4 sensors involved, namely HRVIR and VEGETATION and a quick description of the data which have been used. Then, the processing applied to the data as well as its improvement are related. The computations provide 3 curves : the MTF across the track (along the rows of the images), the MTF along the track (along the columns of the images) and the MTF for the 45° direction. The VEGETATION MTF curves obtained are presented and compared to the pre-flight measurements. This enables to conclude to the good stability of the sensor and to suggest further work.