Ritonavir is an antiretroviral of the protease inhibitor class. It is used against HIV infections as a fixed–dose combination with another protease inhibitor, ritonavir (lopinavir/ritonavir). In the current research, the stimulated FT–Raman biospectroscopy of liquid sample of Ritonavir was investigated. The stimulated FT–Raman diffractions emitted through focusing the second harmonic laser beam Nd:YAG into the sample were recorded by Echelle spectrometer and ICCD detector. Increasing the energy of laser beam from 2.6 (mJ) to 16 (mJ) was led to increase in stimulated FT–Raman signal but after breakdown threshold of liquid sample, more increasing of energy was led to decrease in stimulate FT–Raman signals and for energies higher than 20 (mJ), they were disappeared.