A method for correcting the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) out-of-band (OOB) effects in the Level-1B radiance data product through a multispectral decomposition transform (MDT) is described. The crosstalk information contained in multichannel spectral radiometer data provides the possibility of using the MDT technique to make the corrections. An MDT matrix for the SeaWiFS optical system is derived from the laboratory-measured filter transmittance functions. The OOB correction can be performed by a product between the SeaWiFS MDT matrix and a multispectral image vector. Performance of the SeaWiFS MDT method for the OOB correction is demonstrated by simulation results using hyperspectral data measured with both the AVIRIS and Hyperspectral Imager for the Coastal Ocean sensors. This OOB correction technique is very different from that currently implemented in the operational SeaWiFS data-processing software package.