Fluorinated amino acids are playing an important role in understanding protein-protein interactions, protein folding and protein structure function. Since histidine contains an imidazole ring, we considered the N1-H and N3-H tautomers of 2F-histidine and 4F-histidine, 2F-imidazole and 4F-imidazole, and calculated free energies and 19F NMR shifts in water and acetonitrile. The calculations were performed by the COSMO solvation model with B3LYP method 6-31++G(d) using Gaussian09 software. The calculations showed that the relative stabilities of the four isomers of fluorohistidine are consistent in both the solvents. The same trend is observed for fluoroimidazole isomers.The 19F NMR calculations showed different chemical shifts from zwitterionic/neutral to protonated forms for N1-H and N3-H tautomers of fluorohistidine and fluoroimidazole.