The reaction mechanism and kinetics of chemical reduction of silver were studied in this work by measuring the pH and silver concentration as functions of reaction time. The main objective here is to elucidate the role of alkaline ion in the synthesis of nanosized silver colloids using either formaldehyde or dextrose as the reducing agent. On the reaction mechanism, it was proposed that alkaline ion reacted initially (the first stage) with silver ion to form Ag2O, which was instantly converted to silver and the solution became acidic as a result. During the second stage, silver ion decreased gradually and continuously. Its rate of decrease was shown to follow the [Ag+](2/3) kinetics with an apparent activation energy of about 15.0 kcal mol(-1) for both dextrose and formaldehyde systems. Moreover, it was also found that the values of rate constant from silver kinetics were proportional to the quantity of NaOH added at the beginning of these reactions. (c) 2005 Elsevier B.V. All rights reserved.