In this experimental study, a kinetic model has been developed for Fischer-Tropsch synthesis reactions by using sol-gel technique and Fe/Ni/Al2O3 as the catalyst (40% Fe/60% Ni/40 wt.%Al2O3) in a differential fixed-bed micro reactor assuming no internal or external diffusion. Operating conditions of the reactor were as follows: total pressure 1-12 atm; Temperature 220-260 degrees C; H-2/CO feed ratio 1.5-2; gas hourly space velocity 2100-7000 cm(3)(STP)/h/g(cat) and conversions of 6-37% of hydrogen and 7-21% of carbon monoxide. Mass transfer limitations were investigated by changing synthesis gas velocity in reactors which differ in size. Based on the hypothesis that water inhibits the intrinsic Fischer-Tropsch (FT) reaction rate in the iron-FT synthesis, all rate expressions in this study were in inverse ratio to number of vacant sites and CO and water content. The obtained data in this study were checked using "complete form of Langmuir-Hinshelwood-Hougan-Watson (LHHW)" which has been proposed by Van der Laan and Botes. The kinetic parameters were determined using Levenberg-Marquardt (LM) method. The activation energy and heat of adsorption of CO and water were 103.81, -56.82 and -25.62 kJ/mol, respectively. (C) 2012 Elsevier B.V. All rights reserved.