Inorganic potassium dihydrogen phosphate (KDP) is widely known for its value as a nonlinear optical material. In this study, pure and l-arginine–doped KDP single crystals were grown by the slow solvent evaporation technique and further subjected to infrared absorption and Raman studies for the confirmation of chemical group functionalization and possible bonding between the organic and inorganic materials. The appearance in the infrared absorption spectra of additional vibrational lines, which mostly originate from disturbed N–H, C–H, and C–N bonds of the l-arginine–doped salt, confirm the interaction between KDP and the organic material. This affirmation is supported by more evidence from Raman measurements, where the disappearance of NH vibrations of the amino group is observed. We are thus led to the possibility of hydrogen bonding primarily between the nucleophilic O− of the phosphate unit of KDP and the amino group of the l-arginine.