The present invention relates to a gravity-driven fraction separator and method thereof. The gravity-driven fraction separator is substantially a substrate having a microchannel structure arranged thereon, in which the microchannel structure is extending longitudinally on the substrate while sloping with respect to the level of the substrate by a specific angle. As a micro fluidics is being filled in a loading well situated upstream of the microchannel structure, the micro fluidics is driven by gravity to flow downstream in the microchannel structure while filling a plurality of manifolds formed in a area situated downstream of the microchannel structure, so that accurate quantification and separation of the micro fluidics using the plural manifolds, each having a specific length, can be achieved and provided for posterior inspection and analysis.