Abstract: Terahertz time-domain spectroscopy (THz-TDS) technique is a new technology that can be used for non-destructive testing (NDT), research of molecular dynamics, the nature of crystal, structure and conformation of biological molecules etc. In this work, based on THz -TDS technique, antibiotics of four representative penicillin antibiotic drugs (sulbenicillin sultamicillin, mezlocillin, ticarcillin) were investigated. THz spectral features of antibiotics were studied with the method of both experimental measurement and theoretical analysis. This material was identified through testing the absorption and index of refractive. The experimental results show that the absorption spectra of the four antibiotics between 0.40 -1.60 THz are obviously different, which are therefore the fingerprints of them. The research indicates that THz -TDS technique is very suitable for the detection of antibiotics which have slight difference in chemical structure, and the antibiotic medicine can be distinguished clearly by their THz fingerprint spectra.