A filter medium is provided. According to one embodiment of the present invention, the filter medium is implemented by including: a porous second support and a nanofiber web which are sequentially stacked on each of an upper portion and a lower portion of a first support; and a channel through which a filtrate filtered in the nanofiber web flows in a direction of the first support, wherein the first support, the second support, and the nanofiber web satisfy predetermined conditions on a basis weight and a thickness of each layer. In a water treatment operation of the filter medium, the shape, structural deformation, and damage of the filter medium can be minimized, excellent filtration efficiency can be implemented, and a channel can be smoothly secured, thereby securing high flux. In addition, even at high pressure applied during backwashing, the filter medium has an extended use period due to excellent durability of the filter medium. Accordingly, the filter medium can be variously applied in various water treatment fields.