Gas diffusion layers (GDLs) coated with a hydrophobic microporous layer (MPL) have been commonly used to improve the performance of polymer electrolyte fuel cells (PEFCs). In the present study, a GDL coated with an MPL containing hydrophilic carbon nanotubes (CNTs) was developed to achieve further enhancement of the PEFC performance under both low and high humidity conditions. The less hydrophobic pores formed primarily by the CNTs are effective at conserving the membrane humidity, which enhances the performance under low humidity conditions. The MPL containing the CNTs is also effective at expelling excess water from the catalyst layer. This allows the maximum pore diameter to be decreased to 5 μm without reducing the ability to prevent flooding, resulting in a much higher performance under high humidity conditions compared with that for a hydrophobic MPL coated GDL.