A TiO
_{2}
-coated optical fiber photoreactor was built and studied in order to optimize different parameters before the development of a multi-optical fiber reactor. The physico-chemical properties of the TiO
_{2}
film prepared by a sol-gel method on an optical fiber were first determined. A thickness of about 30 nm per layer and a roughness of 2 nm were estimated by ESEM and AFM, respectively. The refractive index of the TiO
_{2}
coating was determined by a simulation method. Then, the influences of the film thickness, coating length and coating volume on the light transmission within the fiber were investigated. The intensity of transmitted light was found to decrease exponentially as the volume of TiO
_{2}
increased. Afterward, the dependence of the photocatalytic degradation of hydroxybutanedioic acid on the incident light intensity, the TiO
_{2}
coating thickness and the coating volume was studied and modelized. The photocatalytic degradation was found to be stabilized above a TiO
_{2}
volume of 200 μ m
^{3}
for a fiber of 1 mm and 100 μ m
^{3}
for a fiber of 0.6 mm. Finally, a multi-fiber reactor was built and its degradation rate of hydroxybutanedioic acid was compared to that obtained in a single optical fiber reactor.
