A fluid treatment apparatus particularly for sterilizing drinks comprises an elongate tubular duct (110) and an elongate UV light source (111) extending longitudinally of the duct (110). The fluid flows longitudinally of the duct (110) in a thin annular low passage (114) which extends around the UV light source (111). A mixing device (112) disposed between adjacent longitudinal portions of the duct (110) for diverts all of the fluid flowing along a first portion of the passage (114) through fluid mixing means (113,116) in the device (112) and returns the mixed fluid to a second portion of the passage (114). Micro-organisms in the thin flow of fluid are killed as they come within close proximity of the light source (111). The mixing device (112) causes all of the flow to be thoroughly mixed and returned to the flow passage (114). The provision of a plurality of mixing devices along the length of the duct (110) increases the likelihood that all microorganisms receive a sufficient lethal dose of UV radiation.