The influence of copper loading on the surface species and catalytic properties of Fe-Cu-K-La/SiO2 catalyst in the formation of oxygenated by-products during Fischer-Tropsch synthesis was investigated by temperature-programmed reduction (TPR), temperature-programmed desorption of CO and acetaldehyde (CO-, acetaldehyde-TPD), in situ diffuse reflectance FTIR and chemical trapping. The results showed that addition of copper improved the reducibility of catalysts, however, the adsorption features of catalysts changed significantly. Fe-Cu-K-La-SiO2 with a composition of 1:0.28:0.05:0.05:0.17 (molar ratio, relative to iron) had highest selectivity for hydrocarbons and lowest selectivity for C-2 (+) oxygenates. Results of FTIR and chemical trapping indicated that extra copper would suppress CO adsorption as well as oxidation of adsorbed molecules. The stability of intermediates weakened simultaneously. Moreover, the quantitative estimates of the concentration of the surface species by acetaldehyde-TPD allowed the illustration of copper effect on the catalytic properties. FTIR spectra of adsorbed species formed from CO + H-2 interaction on Fe-K-La/SiO2 catalyst with different copper loadings: (a) 0.08; (b) 0.18; (c) 0.28; (d) 0.31; (e) 0.48: (A) 553 K, 3.5 MPa; (B) spectra after switching to pure H-2. In-situ reaction was investigated which confirmed the results obtained in previous characterization including CO hydrogenation reaction, temperature-programmed desorption of adsorbed CO and acetaldehyde (CO-, acetaldehyde-TPD), in situ diffuse reflectance FTIR of methanol and acetaldehyde adsorption and chemical trapping. It could be seen that extra copper caused no apparent changes toward hydrogen which pointed to an unfavorable mobility of products formed on the catalytic surface and could be associated with the reduced reactivity of adsorbed molecules and weakened stability of intermediates with high copper loadings.