Silica protected CuNi bimetallic nanoparticles (CuNi@SiO2) were successfully prepared by a modified co-reduction method. Typically, ammoniacal Cu(II) and Ni(II) were firstly dispersed and encapsulated inside silica by the method of reverse microemulsion. Then, ultra small CuO and NiO particles were in-situ formed during calcination under air. CuNi bimetallic nanoparticles were obtained by the co-reduction of CuO and NiO under H-2 at high temperature. The composition and size of CuNi bimetallic nanoparticles was tuned simply by varying the concentration of precursor solutions. The samples were characterized by FT-IR, TEM, XPS, XRD and ICP-OES. The reduction of p-nitrophenol by NaBH4 was chosen as model reaction to evaluate the catalytic activity. The results indicate that CuNi bimetallic nanoparticles prepared by our method show size and composition dependent catalytic activity. The activation energy of Cus(4)Ni(46)@SiO2 for the same reaction was calculated as to be 16.6 kJ/mol which was much lower than that of Cu@SiO2 (29.0 kJ/mol) and Ni@SiO2 (39.5 kJ/mol). (C) 2016 Elsevier Inc. All rights reserved.