Abstract: By using full-immersion transducer measurement (FITM), a broadband sound speed and attenuation measurement method is presented, which provides a way to obtain the sound speed and attenuation of ultrafine sediments (average particle size of 5.27 µm and porosity of 79%) in laboratory. The dependence between sound speed and attenuation was compared with Kramers-Kronig relation for confirming the reliability of the in-lab measurement. Meanwhile, Hamilton classic curves indicate that the in-lab measurement results meet the speed-porosity relation, and the attenuation from the in-lab method is within the confidence interval of Hamilton curves. The sound speed and attenuation prediction curves of the effective density fluid model and the grain-shearing model are satisfied which also proves the accuracy and availability of the in-lab measurement method.