ZrHEDPs, zirconium phosphonate functionalized with -PO3H2s moieties, were synthesized to overcome the humidity dependence of proton conductivity, the serious drawback of proton conducting materials. As the P/Zr in ZrHEDPs increased, they had more packed-PO3H2 moieties and exhibited a higher proton conductivity with a lower reliance on RH. Notably, the proton conductivity of the ZrHEDP pellet with P/Zr = 3.0 at 95% RH only decreased to 2/3 at 40% RH, whereas Nafion at 40 % RH shows 1/5-1/20 of its conductivity at 95% RH. The low RH dependence is an ideal property for several applications, such as PEFC applications.