The absolute configuration of the Saquinavir myselate has been determined. The structural analysis confirms the absolute stereochemistry for (2S)-N-[(2S, 3R)-4-[(3S)-3-(tert-butylcarbamoyl)-decahydroisoquinolin-2-yl]-3-hydroxyl-1-phenylbutan-2-yl]-2-(quinolin-2ylformamido) butanedia midemyselate. Saquinqvir myselate exhibits monoclinic crystal system and P21 space group with unit cell dimensions of α=90 0 ,β= 114.848(2)0 and γ=900Stereochemistry observed using platon is N(1)-S, C(2)-S, C(7)-S, C(9)-S, C(16)-R, C(17)-S and C(26)-S.