Palladium nanoparticles (Pd NPs) supported on the surface of sodium dodecyl sulfonate (SDS)-intercalated layered double hydroxide (LDH) nanocomposites were synthesized by a one-step, facile ultrasonic method. The Pd/SDS-LDH nanocomposites were characterized by UV-visible spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, N-2-adsorption, Fourier transform infrared spectroscopy, and inductively coupled plasma optical emission spectrometry. The Pd NPs had an average size of 3.56 nm and were uniformly dispersed on the SDS-LDHs surface. The conversion of 4-bromotoluene catalyzed by Pd-0.02/SDS-LDHs reached 98.16 % with 0.1 mmol % catalyst at room temperature without any phase transfer agents, toxic solvents, or inert atmosphere; this conversion was much higher than that of Pd-0.02/SDS-LDHs prepared without ultrasound. This was attributed to the high dispersion and size uniformity. Notably, Pd-0.05/SDS-LDHs had a much higher catalytic activity than that of commercial Pd/C catalyst with the same Pd content due to the strong interaction between the Pd species and the SDS-LDHs in the Pd/SDS-LDH nanocomposites. These catalysts could be easily separated by centrifugation, and could be recycled five times with little activity loss.