¹³C NMR spectroscopic method has been applied to determine the pKa of carboxylic acids. Anasazi EFT 60 MHz FT-NMR Spectrometer was used to perform the project because deuterated solvent was not required for the instrument. All the carboxylic acid solutions of various pHs were prepared with HCl and NaOH solutions of corresponding carboxylic acid, and their spectroscopic data have been obtained with the aqueous solutions. The pKa of carboxylic acids determined by ¹³C NMR spectroscopic method have been compared with the corresponding literature values.