A filter assembly including a filtration medium comprising a nanofiber, having a three-dimensional network structure, and having a fiber web layer comprising a hydrophilic coating layer that covers at least a part of the outer surface of the nanofiber; and a first support body that supports the filtration medium, which is provided on both surfaces thereof, and has a channel formed therein. Accordingly, the filtration medium has excellent chemical resistance and improved hydrophilicity such that the flow rate can increase substantially. In addition, the improved hydrophilicity is maintained for a long period of time such that the utilization period can be extended substantially. Furthermore, any change in the pore structure of the filtration medium during the hydrophilicity endowing process is minimized such that the initially designed physical characteristics of the filtration medium can be fully exhibited.