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 ATR–FTIR biospectroscopy of liquid sample of Ritonavir was investigated. The stimulated ATR–FTIR 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 ATR–FTIR signal but after breakdown threshold of liquid sample, more increasing of energy was led to decrease in stimulate ATR–FTIR signals and for energies higher than 20 (mJ), they were disappeared. Skeletal formula of ritonavir (original trade name Norvir)—an HIV protease inhibitor and a pharmacokinetic booster. Orientation made to match to show the structural similarity between ritonavir and cobicistat. Created with ChemDoodle 8.0.0.b1 and Adobe Illustrator CC 2015.