First-principles calculations based on Density Functional Theory have been done on an important amino acid Â L-allo-isoleucine:D-leucine which is also known as (S,R)-2-amino-3-methylpentanoic acid:R-2- amino-4-methylpentaoic acid. Its structure has been simulated. The unit cell is triclinic with lattice parameters a=5.236Å, b=5.425Å and c=13.573Å showing a space group of P1. Bond lengths and bond angles have been estimated. Electronic Density of States calculations show that the material has a band gap of 4.16eV. Electronic band structure indicates that the material can be effectively used for NLO applications. The dielectric constant has been calculated and its value comes out to be 2.26, 2.22 and 2.13 along X, Y and Z axes respectively and its average value comes out to be 2.20. Phonon modes at gamma point have also been computed in L-allo-isoleucine:D-leucine and they range from 88cm- 1 to 5782cm-1.