The present invention relates to process for preparation of optical resolution of substituted 2-(2-pyridinylmethylsulphinyl)-1H-benzimidazoles either as a single enantiomer or in an enantiomerically enriched form. Thus, for example, R-1,1'-binaphtyl- 2-2'-diyl hydrogen phosphate was reacted with 2-[[[3-methyl-4-(2,2,2-trifluoro-ethoxy)- 2-pyridinyl]methyl]sulfinyl]-1H-benzimidazole (Lansoprazole) in a mixture of benzene and cyclohexane to obtain diasteremeric complexes. The diasteremeric complexes were subjected to fractional crystallization to obtain R-2-[[[3-methyl-4-(2,2,2-trifluoro- ethoxy)-2-pyridinyl]methyl]sulfinyl]-1H-benzimidazole.R-1,1'-binaphthyl-2-2'-diyl hydrogen phosphate. The separated isomer was treated with sodium bicarbonate in a mixture of ethyl acetate and water to obtain R-2-[[[3-methyl-4-(2,2,2-trifluoro-ethoxy)-2- pyridinyl]methyl]sulfinyl]-1H-benzimidazole (dexlansoprazole).