Photocatalytic disinfection using TiO2 particles suspended in a reactor involves two major problems; the exponential decrease of light availability due to the scattering of UV light by particles themselves and the difficulty of recycling particles. To resolve these problems, scratched optical-fibres, inserted in glass tubes were used to diffuse UV Light uniformly in a reactor. Comparative disinfection studies using these optical-fibres were done in both cases of suspended and immobilised photocatalysts. Disinfection capability with the immobilised photocatalysts at 4.9 muE s(-1) dm(-3) was twice that of the slurry reactor. Survival ratios of less than 0.2 were obtained with a residence time of 50 min and an initial cell concentration of 10000 cfu cm(-3) in the 6 dm(3) plug-flow type reactor.