Sound velocity and attenuation measurements in unconsolidated marine sediments have been made by a resonance method which utilizes a thin-walled plastic cylinder as a pressure-release container to hold samples. Velocities were determined from resonant frequencies which lay between 23 and 36 kc/sec for the 2 inch diameter by 4 inch long cylindrical container used. Attenuation was determined from the sharpness of the resonant modes. Relatively undisturbed sediment samples were obtained by diver, in shallow water, using the same plastic containers in which the acoustic measurements are made. Deep sea samples were obtained by cutting sections from cores which were taken in plastic tubes.Velocities for shallow water sediments in the San Diego area ranged from 4,840 ft/sec (0.978 times sea water velocity) for fine silt to 5,680 ft/sec (1.147 times sea water velocity) for medium sand, measured at 60 degrees F. and atmospheric pressure. Velocities in deep-sea red clay samples ranged between 0.980 and 1.040 times the sea water velocity, at 60 degrees F. and atmospheric pressure. Attenuation coefficients for shallow-water San Diego sediments varied from about 1 to 4 db/ft for silts, to about 3 to 8 db/ft for sand.