Abstract: The mechanism of the reaction between cefaclor (CFC) and bovine hemoglobin (BHB) in a buffer solution of Tris-HCl (pH 7.40) was studied by fluorescence quenching and synchronous fluorescence spectrometry at different temperation conditions of 293 K, 303 K and 310 K. It was shown by the results that the fluorescence intensities obtained from both the fluorometry and the synchronous fluorometry were decreased regularly as the concentrations of CFC were increased, indicating that a coordinative complex was formed between CFC and BHB and that CFC showed a static quenching effect on the fluorescence of BHB. Only tryptophane radical of BHB was found to take part in the complexation reaction, and the number of binding site was found to be about one. Base on the analytical study of the thermodynamic parameters of ΔH, ΔS and ΔG, it was found that electrostatic action was the main force of the reaction. As shown by the expermental results, values of drug binding rate (w_Q) of CFC were decreased with raise of reaction temperature, e.g., as the temperature raised from 293 K to 310 K, values of w_Q decreased from 94.08% to 93.14%, with the values quite large. It meant that the binding of CFC with BHB, made it possible for BHB to deliver CFC effectively to the focus of infection. It was also shown that values of protein binding rate (w_B) were kept almost unchanged with the raise of reaction temperatures (w_B 0.577% to 0.571%), with the values quite small. It meant that the free concentration of BHB was not affected by the combination of CFC with BHB, i.e., the oxygen conveying function of BHB was kept in normal state.