In the frame of the JERS1 System Verification Program, conducted by MITI-NASDA, CNES and CERT proposed to use the knowledge of the SPOT high resolution sensors (HRV) calibration to deduce the in-flight calibration of the visible and near infrared bands of the JERS1 optical sensor (OPS). The idea is to perform an intercalibration of the cameras using close in time acquisitions over stable desert areas, regularly acquired for SPOT/HRV multitemporal calibration studies. In spite of operational difficulties to achieve such a 'rendezvous', it has been possible to obtain a cloud free OPS acquisition over one of our SPOT sites with a couple of SPOT3 acquisitions, two days before and three days after the JERS1 overpass. This paper describes in detail the method used to perform this intercalibration and its estimated accuracy. Such a method, already experimented with other satellites, provides a good intercalibration useful for a combined use of SPOT and JERS1 data. As far as OPS absolute calibration is concerned, discrepancies of 14 to 17%, according to the spectral band, can be noticed in comparison with the absolute calibration coefficients provided with the image data which could indicate a sensitivity decrease of the sensor from the ground measurements.