In this study, the transformation mechanism of cefalexin (CFX) via TiO2 photocatalysis and the roleof humic acids extracted from two agro-industrial residues, coffee (HAc) and rice (HAa) husks wereevaluated. During the TiO2 photocatalysis, 90% CFX degradation was found after 180 min ofirradiation (365 nm); in the presence of HAc and HAa, 37% and 61% CFX degradation wereobserved, respectively. This shows that the extracted humic acids do not promote the formation ofreactive oxygenated species; further, they act as scavengers of hydroxyl (.OH). Additionally, it wasfound that CFX degradation by heterogeneous catalysis with TiO2 is mainly associated with holeoxidation (47%) and it is caused by •OH radicals in solution (38%). Finally, we can conclude that therole of humic acids as photosensitizers or scavengers is related to their structural properties.