Abstract: A simple method for computing drug absorption rate constant k_a has been suggested. The method utilizes characteristic values of drug blood concentration-tlme curve (the peak value, the time needed to reach the peak value and the inflectional value) to calculate k_a directly. The formula for calculation is as follows:(1) where K is the drug elimination rate constant.Theoretically, for one-compartment open model, use formula (1) to calculate k_a is correct, while for two-compartment model, it only gives a rough estimate of k_a. Actually, accuracy of k_a calculated according to formula (1), is not only dependent on compartmental model but also dependent on other parameters involved.