TiO2 nanoparticles coated cotton fiber composite was successfully prepared by using a sol-gel method at low temperature (about 100°C) using tetrabutyl-titanate [Ti(OBu)4] as raw material. The preparation of the TiO2 colloid and the composite were described. The properties of resulting materials were characterized by SEM and XRD, the photocatalytic degradation performance was tested using methylene blue (MB) as the target pollutant in aqueous solution. The results showed that the amorphous TiO2 nanoparticles were distributed evenly on the outer surfaces of cotton fibers, which shows efficient photocatalytic properties when exposed to UV light, the degradation rate of MB reached 95.35% under the conditions of catalyst dosage 2.5 g/L, MB concentration 50 mg/L, irradiation time 120 min, and pH 10, and the photocatalytic activity of TiO2/cotton fibers remained above 90% of its activity as-prepared after being used four times, the degradation rate of MB could reach 88.78% when irradiation time was 120 min. The photocatalytic degradation of MB could be properly described by the first-order kinetic law. By comparison of the removal rates of MB with and without UV light, it could be affirmed that the disappearance of MB was due to photodegradation rather than adsorption on cotton fibers.