Imaging tumoral pH may help to characterize aggressiveness, metastasis, and therapeutic response. We report the development of hyperpolarized [2-¹³C,D₁₀]diethylmalonic acid, which exhibits a large pH-dependent ¹³C chemical shift over the physiological range. We demonstrate that co-polarization with [1-¹³C,D₉]tert-butanol accurately measures pH via¹³C NMR and magnetic resonance spectroscopic imaging in phantoms.