Experiments for the kinetic of Fischer-Tropsch reaction (hydrocarbon formation) have been carried out over the potassium-promoted Co-Fe/90wt % SiO2 catalyst in a fixed bed micro-reactor over a range of operating conditions. Reaction rate equations are derived on the basis of the Langmuir-Hinshelwood-Hougen-Watson (LHHW) type models for the FT reactions. Seven kinetic expressions for CO consumption have been proposed and interaction between adsorption CO and dissociated adsorption hydrogen as the controlling step give the most plausible kinetic model. The product distributions in FT synthesis are found to be strongly influenced by temperature and pressure, and optimum hydrocarbon selectivity C-2-C-3 light olefins is obtained at 260 degrees C and 8 bar. The value of activation energy for CO consumption confirms that intraparticle mass transport is not significant.