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Tannins are recalcitrant polyphenolic molecules that resist microbial attack. Their main environmental damage is due to their low biodegradability. This work aims to investigate the photo-catalytic degradation of two commercial tannins extracts, Chestnut (hydrolysable tannin) and Mimosa (condensed tannin). The experiments were carried out under UV-light irradiation in a continuous-flow reactor using titanium dioxide (TiO2) immobilized on cellulosic fibers. It was highlighted that photo-degradation is unfavourable in acidic medium and when the pH is too high (pH above 12), it reaches its maximum efficiency at pH 7.5 (99 and 97% for Chestnut and Mimosa, respectively). Nearly complete degradation of tannins requires an irradiation period of 6 h. Photo-degradation efficiency is inversely affected by the concentration of tannins essentially beyond 75 mg/L for Chestnut and 60 mg/L for Mimosa. Above 240 mL/min, any increase in feed flow negatively affects the performance of the process. On the other hand, a significant decrease of photo-degradation efficiency was seen when increasing the concentration of ethanol and salts in the medium. Obtained results suggest that UV-light irradiation in a continuous-flow photo-reactor using immobilized TiO2 may be considered as an adequate process for the treatment of water containing recalcitrant tannins molecules.