Pharmacokinetic behavior of β-lactam antibiotics (cefodizime and cefotetan) in humans were predicted from the animal data. Total body clearance (CL_p) of these drugs in humans (weighing 65-69 kg) were successfully extrapolated from the allometric relationship between the clearance for the unbound drug in plasma and body weight (r=0.954-1.000) with a power of 0.948-0.991 for cefodizime and 0.700-0.756 for cefotetan. We also predicted the volume of distribution at steady state (Vd_ss), the volume of distribution in the central compartment (V₁) and the volume of distribution at β-phase (Vd_β) of these drugs in humans from the observed human plasma unbound fraction, inasmuch as the plasma unbound fraction correlated well (r=0.913-0.995) with the values of Vd_ss, V₁, and Vd_β among various animal species. Based on these predicted pharmacokinetic parameters, we calculated the plasma concentration profiles of these drugs in humans and found a good agreement between the predicted and observed values. We also report here that the prediction is successful when we consider the plasma protein binding of these drugs.