This paper proposes a new concept of 'Inverse Streamline Mapping for Finding an Optimum Medicine Injection Point in Micro Chamber'. We search the streamlines from the target chamber to the point in the cross-section at the entrance, so that we can find an optimum medicine injection point. The optimum condition is that all streamlines in target chamber start from the smallest cross-sectional area for a given microfluidic chip. The idea is enhanced by designing the microfluidic channel with the desirable streamline mapping between the target chamber and the cross-section at the entrance. We show that the liquid supplied at a particular point can fully cover the chamber in both simulations and experiments.