OBJECTIVE This study aimed to explore the chemical changes and discoloration of endodontically treated teeth using spectroradiometric and chemical analyses. METHODS Ten freshly extracted sound third molars and 10 discolored molars obtained after root canal treatment (RCT) were included in this study. Dentin blocks (3 × 3 × 1 mm) were prepared and treated with an intracoronal bleaching agent. Spectroradiometric evaluations, X-ray photoelectron spectroscopy (XPS), and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) analyses were performed before and after bleaching. The spectroradiometric parameters and XPS and ATR-FTIR spectra of the dentin slabs were analyzed using independent-sample t-tests or one-way analysis of variance. RESULTS Differences in color coordinates and translucency parameters were observed between the two groups before bleaching. Demineralization effects were also detected in the discolored dentin. No binding energy shifts or new spectral bands were found in the XPS and ATR-FTIR spectra, except in the narrow-scanned XPS spectra of C1s. Significant changes in color coordinates were also found in both groups after bleaching, and the translucency parameter was remarkably altered in discolored dentin. The organic and inorganic components of dentin also decreased in both groups. However, binding energy shifts (ie, C1s, Ca2p, and P2p) were detected only in discolored dentin. CONCLUSIONS Significant alterations in the organic and inorganic components of dentin contributed to the discoloration of endodontically treated teeth. Moreover, intracoronal bleaching could effectively whiten both discolored and vital dentin. The chemical compositions of mineral and organic components within discolored dentin are more sensitive to the acid bleaching agent than normal teeth.