The frequency dependence of the sound speed and attenuation in seafloor sediments was measured in a laboratory by using a probe method at the frequency range of 25-250 kHz. The standard deviation of repeated sound speed measurement in fresh water is about 2.82 m/s. Repeated measurement of attenuation shows a minimum standard deviation of 0.58 dB at 25 kHz and a maximum standard deviation of 3.06 dB/m at 250 kHz. The measurement results indicate that the sound speeds vary from 1638 to 1658 m/s in sandy silt sediments and from 1548 to 1571 m/s in clayey silt sediments. The attenuation increases from 14.2 to 51.9 dB/m in sandy silt sediments and from 7.8 to 31.7 dB/m in clayey silt sediments. The measured sound speed dispersion in sandy silt sediment agrees reasonably with the predictions of the Biot-Stoll model, the Grain-Shearing model, and the Effective Density Fluid model (EDFM). The measured sound speed in clayey silt sediment agrees better with the predictions of the GS model than that of the Biot-Stoll model and the EDFM. The measured attenuation is more consistent with f(1/2) dependence than the f(1) dependence, and is similar to the predictions of Biot-Stoll model and the EDFM.