This study combined Fourier transform-near infrared (NIR) spectroscopy and chemometrics, to monitor changes in peptide content during the solid-state fermentation of rapeseed meal. A NIR calibration model was established by performing spectral scanning on 81 samples and using interval partial least squares. The results showed that coefficient of determination (R2) and root mean square error of cross-validation could achieve 0.9441 and 0.654 g/L for polypeptide content. Furthermore, the predicted and experimental values of the two parameters in an external validation set showed similar changes throughout the fermentation.