Provided is a novel method capable of conveniently and rapidly testing sensitivity of a bacterium or a fungus to an antibacterial drug, and a testing system used for the method. This testing method is a method for testing antibacterial-drug sensitivity of a bacterium or a fungus, and is characterized in including: a step for using a micro-device having a flow channel, and incubating inside the flow channel of the micro-device a mixture of an antibacterial drug and a bacterium liquid to be tested; and a detection step for detecting a bacterium or fungus derived from the bacterium liquid to be tested, in an observation area of the flow channel of the micro-device. The detection step can be performed by detecting in the observation area, using a microscope or the like, e.g., any increase/decrease or morphological change in the bacterium or fungus derived from the bacterium liquid to be tested.