The Moderate Resolution Imaging Spectroradiometer (MODIS) is one of the five Earth-observing instruments onboard the NASA EOS Terra spacecraft launched in December 1999. It makes frequent global observations over a broad spectral range (0.41 to 14.4μ) and at three spatial resolutions (0.25km, 0.5km, and 1km at nadir). The MODIS was designed with a set of on-board calibrators (OBCs) that include a solar diffuser (SD), a blackbody (BB), and spectro-radiometric calibration assembly (SRCA). One SRCA function is to provide on-orbit spectral characterization of the MODIS reflective solar bands (RSB) with wavelengths from 0.41 to 2.2μ. This paper provides an overview of the MODIS SRCA on-orbit spectral characterization approach and summarizes the results derived from five years of Terra MODIS on-orbit observations. In general, the on-orbit characterization of the Terra MODIS RSB relative spectral responses (RSR) has been satisfactory. The measured center wavelength (CW) shifts are less than 0.6nm for the 412nm spectral band, 0.5nm for the 443nm band, and 0.4nm for the remaining reflective solar bands (short-wave infrared bands excluded). The bandwidth (BW) changes are typically less than 1nm. Excluding the differences between pre-launch and initial on-orbit results, the CW shifts and BW changes are very stable. For a given band, the detector-to-detector spectral characterization differences are typically less than 0.2nm.