The water-soluble polyallylamine (PAH) functionalized tetrahedral palladium nanocrystals with adjustable size and concavity are successfully achieved through a one-pot hydrothermal synthesis. The size, morphology and surface composition of tetrahedral palladium nanocrystals are investigated by transmission electron microscopy (TEM), high angle annular dark field scanning TEM (HAADF-STEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS). The anchorage of PAH on palladium nanocrystals results in excellent colloidal stability and anti-oxidation capability of palladium nanocrystals. Both {1 1 0} and {1 1 1}-enclosed concave tetrahedral palladium nanocrystals (c-Pd-TNCs) exhibit superior catalytic activity to only {1 1 1}-enclosed flat tetrahedral palladium nanocrystals (f-Pd-TNCs) for the hydrogenation reduction of nitro functional groups and C=N double bond. (C) 2013 Elsevier B.V. All rights reserved.