Disclosed herein is a plastic microchip used in counting the number of microparticles and a method for manufacturing the same and, more particularly, to a plastic microchip including a negative microgrid pattern formed on a lower substrate, a solvent channel and solvent inlets for a solvent welding process, and a method for manufacturing the plastic microchip by injection molding the lower substrate on which a negative microgrid pattern is formed and by injecting a solvent through the solvent inlets so as to fix an upper substrate to the lower substrate.
According to the present invention, it is possible to form a microgrid pattern of a relatively narrow width deeply and uniformly as a negative microgrid pattern is formed on the lower substrate and thereby to provide a clear microgrid pattern, thus facilitating accurate observation of microparticles. Moreover, it is also possible to provide a uniform height of an injection chamber by welding an upper substrate and a lower substrate to each other by a solvent welding process, thus ensuring a more accurate analysis result.