Inspection techniques using guided waves require an accurate prediction of the propagation properties and the physical behaviour of the waves. Properties of these guided waves can be modelled using dispersion curves, which are calculated numerically. However, any curvature along the propagation direction can change the behaviour of the modes compared to those in the straight waveguide. There are currently few studies of the curvature effect along the propagation direction of any waveguide problem. We have used a 2D circumferential waveguide problem to study the curvature effect, from which the phase velocity and the mode shapes have been examined at various curvatures. The percentage difference in velocity of the low order plate modes, as a function of frequency and curvature, has been calculated numerically. Furthermore the changes in phase velocity have been correlated with the changes in mode shapes that are due to the curvature effect. This paper also presents an experimental study to validate the analytical predictions. The experiment involved a sensitive measurement of the change of velocity as the curvature of a waveguide was increased. Reasonably good agreement was obtained between the experimental measurements and the predictions. © 2004 American Institute of Physics