Abstract: The bioavailability of eye drops (prepared with saline and buffered solutions) of Bao Gong Teng A(isolated from Erycibe obtusfolia Benth) have been studied by using the pharmacological response(miotic action). The change in pupillary diameter of the rabbit eye is chosen as a graded quantitative pharmacological response to indicate the change of intensity. The observed pharmacological data are converted, via the use of a dose-effect curve, to values corresponding to the relative biophasic drug levels. The relative bioavailability of saline solution of Bao Gong Teng A is computed from the ratio of the total areas under the curves (AUG) plotted with the relative biophasic drug levels of both solutions versus time. The results demonstrate that in comparison with saline solution the relative bioavailability of buffered solution of Bao Gong Teng A is 60% (P<0.05).