This study uses different carbon fiber reinforcing materials impregnated with different phenolic resin concentrations to produce composite materials for use as fuel cell gas diffusion layer (GDL) substrates. Because of the differing structures of various carbon fiber reinforcing materials, GDL substrates made from these materials display different characteristics. For instance, GDL substrates produced from oxidized carbon felt have a relatively loose structure and can absorb a large quantity of resin; the properties of this type of substrate may change significantly with resin content. In contrast, the weave structure of oxidized carbon cloth tends to lessen the influence of the impregnated resin content. With regard to fuel-cell performance, GDL substrates fabricated from oxidized fiber felt yield the best performance when resin content is 10 wt % and have a limiting current density of as high as 1677 mA/cm(2). A resin content of 2 wt % yields optimal performance when oxidized carbon cloth is the raw material, and the limiting current density can achieve 2207 mA/cm(2).