Biochar is charred material produced by the pyrolysis of organic biomass. In this work, Fourier transform infrared (FTIR) spectra of various agricultural by-products feedstock and their derived biochars were collected to explore the potential of FTIR technique as a simple and rapid method for characterizing their biochar structure. The FTIR information was also discussed for comparing the biochar formation process. Biochars became increasingly more aromatic and carbonaceous with increase in pyrolysis temperature, and these changes could easily be detected from FTIR spectral differences. Complementary to visual inspection of spectral variations, principal component analysis (PCA) of FTIR spectra enhanced the similarity or dissimilarity of biochars prepared at various temperatures. On the basis of spectral features in the 1750-1500 cm -1 region assignable to characteristic carboxyl and aromatic groups that existed in the starting materials and also in biochars, a simple three-band ratio algorithm was developed to monitor the biochar formation semi-quantitatively. Results indicated the feasibility of FTIR in rapid and non-destructive biochar measurements for quality and production.