In this paper, the biosynthesis study of silver nanoparticles (AgNPs) using chitosan immobilized on the Bacillus cereus (Bc-C) was performed via bioreduction without any reducing agent. Transmission electron microscopy (TEM) showed that the AgNPs were formed as uniformly sized and shaped in the range of 10-30 nm. Scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS) and x-ray diffraction patterns (XRD) confirmed the formation of the Bc-C-Ag. XRD diffraction patterns revealed that the Ag+ on the Bc-C was reduced to Ag (0). This situation shows successful AgNPs synthesis using Bc-C In the bioreduction studies, the effects of operating variables such as initial metal concentration, pH and contact time were also investigated. The AgNPs formed on Bc-C (Bc-C-Ag) were used as a bionanocatalyst for the reduction of 4-nitrophenol (4-NP). The kinetic models and the thermodynamic parameters were investigated to reveal the reduction mechanism. (C) 2013 Elsevier B.V. All rights reserved.