Wheat bran is a massive by-product from agro-industry, which is a sustainable raw material to make carbon material (CM). This work addresses wheat bran as a possible source for leather tanning agents to enlarge its industrial applications. Firstly, wheat bran was extracted with water and further modified with a hydrothermal carbonization (HTC). The UV–vis spectra, the FTIR spectra and the fluorescence phenomena were recorded to speculate the effects of HTC on the components in the bran extract solutions in terms of the reaction time (1 h, 3 h, 5 h and 7 h) at 170 ℃ and the reaction temperature (150 ℃, 170 ℃ and 190 ℃) at 5 h. Secondly, the bran-based CM was directly used to tan pickled pigskins without purification according to a normal leather processing procedure. The maximum rise in shrinkage temperatures of pigskins reached to 27 ℃ after tanning with bran CM. Scanning electron microscope images and atomic force microscope images revealed that bran-based CM penetrated into the collagen fibers to loosen and dilate fibers and then further provide stable crosslinking, resulting in firm and delicately grained surfaces. These results demonstrated that bran-based CM was an effective and environmentally-friendly tanning agent.