Polymer electrolyte-based unitized reversible fuel cells (URFCs) combine the functionality of a fuel cell and an electrolyzer in a single device. In this study, the influence of hydrophobic agent in the gas diffusion layer (GDL) of URFC was investigated. The titanium (Ti)-felt GDL which treated with different percent of PTFE emulsion was intensively tested with various humidification temperature conditions in the single cell of URFC. I-V performance curves and divided three overpotentials were compared and analyzed in the fuel cell mode. The electrolyzer performances were also evaluated with the I-V curves. Experimental results showed that the GDLs with high PTFE contents have better performance in the dry conditions. On the other hand, the increased PTFE contents accelerate flooding problem in the wet condition and it is related with rising concentration overpotential. The electrolyzer performances are almost same with different PTFE contents of GDL.