Abstract: In order to study the transmission of Lamb waves at integral stiffeners in platelike structures, both Finite Element Modeling(FEM) simulations and experiments are conducted. Combined with dispersion curves of Lamb waves and two dimensional Fourier transform analysis, the effects of integral stiffeners with different geometries upon vertically incident Lamb waves are studied. Experiment and simulation results show that stiffeners act like comb filters upon Lamb waves of different frequency components. The passband widths and the number of passbands of comb filters are affected by the geometry of stiffeners:as the height of stiffener increases, the passband becomes narrower and the comb filter has more fluctuations;as the stiffener becomes wider, the number of passband changes not monotonically, which is more complex than the effect of stiffener height;in the case of the same aspect ratio of stiffener, the higher and wider the stiffener is, the more and narrower the passband is. Study results can provide specific guidance on the frequency band selections of Lamb waves in structural health monitoring and nondestructive evaluating application to increase the effective detection range and signal-to-noise ratio of Lamb waves.