Tests have been carried out on one of the advanced gas-cooled reactors (AGRs) at Hinkley Point to determine the fuel temperature coefficient of reactivity, an important safety-related parameter. Reactor neutron flux was measured during transients induced by movement of a bank of control rods from one steady position to another. An inverse kinetics analysis was applied to the recorded flux transient to determine the reactivity change as the fuel temperature changed, and the variation of mean fuel temperature was derived from the flux transient by a multiplane thermal-hydraulics code representing an AGR fuel channel The fuel temperature coefficient was then obtained from the slope of a plot of core reactivity against fuel temperature. The uncertainty to be applied to the derived temperature coefficient has been shown to be approximately ±10% at the one standard deviation level The experimental technique has been found to be simple to apply on a commercial reactor and has given consistent results over a range of reactor operating conditions. Calculations of fuel temperature coefficients of reactivity (based on the lattice code, ARGOSY) have been carried out and reactor averaged values deduced for comparison with experiment. The calculated and measured coefficients agree to within one standard deviation over a range of core irradiations and power levels.