The cross calibration of ocean color satellite sensor, IRS-P4 OCM using the radiative transfer code, with SeaWiFS as a reference are presented here. Since the bands of IRS-P4 OCM are identical to those of SeaWiFS and SeaWiFS has been continuously and rigorously calibrated, SeaWiFS is used as a reference for the cross calibration of IRS-P4 OCM. Calibrations coefficients for each band of IRS-P4 OCM are derived by comparing the actual radiances detected by the satellites at top of the atmosphere and those obtained from the radiative transfer simulations of IRS-P4 OCM and SeaWiFS. The chlorophyll a values derived using the calibrated IRS-P4 OCM are found to be comparable with those derived from SeaWiFS and in close agreement with the measured values. The relative root mean square error (RRMSE) between measured chlorophyll a and those derived from the satellites are found to be 0.28 and 0.26 for SeaWiFS and IRS-P4 OCM respectively