The aim of this study is to investigate the vibrational modes of common ions such as sodium (Na+), potassium (K+), magnesium (Mg2+), calcium (Ca2+) and chloride (Cl−) ions in living organisms by THz spectroscopy. These ions play key roles in intra- and extracellular signaling, cell membrane potential maintenance, neural signaling, regulation of metabolic activities, and cell volume regulation. The results show that each ion displays distinctive absorption peaks, and the positions and intensities of these peaks reflect their respective vibrational modes. The absorption peaks of Na+, Cl−, and K+ are located in the lower frequency region, whereas those of Ca2+ are located in the low frequency region, and the absorption peaks of Mg2+ are more distinctive and located in the higher frequency bands in the low frequency region. By analyzing the positions, intensities and shapes of these characteristic peaks, we are able to infer the chemical environments and possible interactions of the ions, which is essential for understanding the mechanisms of ion action in living organisms.