Abstract: The acoustic attenuation coefficients and velocities of fluid-mud collected from Changjiang Estuary and Hangzhou Gulf respectively have been measured with ultrasonic waves of 4 frequencies (100,150,500 and 1500kHz)in a water tank. The results show that the linear variations of acoustic attenuation coefficients with bulk densities of fluid-mud in the range of 10.0~16.0kN/m³ for a certain frequency and with frequencies for a certain bulk density are confirmed, that the attenuation coefficient of fluid-mud in Hangzhou Gulf is a little more (about 10%) than that in Changjiang Estuary for a certain bulk density at the same frequency, and that the variation of acoustic velocities with bulk densities in the range of 10.0~16.0kN/m³ is slight (about ±2%) and a minimun of velocity can be clearly found at 100kHz and 150kHz frequencies, e.g.1460m/s vs14.5kN/m³ in Changjiang Estuary and 1440m/s vs13.5kN/m³ in Hangzhou Gulf.