Abstract: A fluid sensor comprises a fluid conduit having a wall defining a fluid flow path and an acoustic transducer located externally of the fluid flow path. The wall of the fluid conduit comprises a composite region between the acoustic transducer and the fluid flow path, the composite region comprising a composite material including a polymer matrix material and one or more reinforcing elements embedded within the polymer matrix material. Such a fluid sensor may be used for sensing a property of a fluid and, in particular though not exclusively for sensing a property of a fluid produced from or injected into an oil or gas well.