NOVELTY - Preparation of echothiophate iodide (I) comprises providing a solution of 2-(dimethylamino)ethane thiol or its salt and a base in an organic solvent; optionally heating the reaction mixture at 50-70 degrees C and obtaining a residual mass; treating the material of the first or second step with diethyl halogen phosphate in an organic solvent having boiling point of greater than 100 degrees C to obtain S-2-(dimethylamino)ethyl O,O-diethyl phosphorothioate (II); reacting compound (II) with methyl iodide in an organic solvent; and isolating pure (I).    USE - Preparation of echothiophate iodide (I) i.e. crystalline echothiophate iodide (I) form-SET (claimed) used for pharmaceutical composition useful in the treatment of ocular disorders e.g. glaucoma.    ADVANTAGE - The process is ecofriendly, avoids the use of hazardous solvent systems and provides echothiophate iodide (I) of high purity. It is efficient, cost-effective, industrially scalable and safer for handling and provides the pure non-hygroscopic end product in high yield with better and consistent quality parameters. The echothiophate iodide (I) crystalline form-SET is stable, pure and easy for handling.    DETAILED DESCRIPTION - Preparation of echothiophate iodide of formula (I) comprises providing a solution of 2-(dimethylamino)ethane thiol or its salt and a base in an organic solvent; optionally heating the reaction mixture at 50-70 degrees C and obtaining a residual mass; treating the material of the first or second step with diethyl halogen phosphate in an organic solvent having boiling point of greater than 100 degrees C to obtain S-2-(dimethylamino)ethyl O,O-diethyl phosphorothioate of formula (II); reacting compound (II) with methyl iodide in an organic solvent; and isolating pure (I). INDEPENDENT CLAIMS are included for:    (1) crystalline echothiophate iodide (I) form-SET having X-ray powder diffraction pattern with peaks given in the specification;    (2) preparation of echothiophate iodide (I) form-SET having X-ray powder diffraction pattern with peaks given in the specification comprising providing a solution of 2-(dimethylamino)ethane thiol or its salt and a base in an organic solvent; optionally heating the reaction mixture at 50-70 degrees C and obtaining a residual mass; treating the material of first or second step with diethyl halogen phosphate in an organic solvent having boiling point of greater than 100 degrees C to obtain compound (II); reacting compound (II) with methyl iodide in an organic solvent; providing a solution of the obtained reaction mass in 2-5 volume 1-3C alcohol solvent; recovering solvent from reaction mixture to obtain a residue; treating the residue with an ester solvent to isolate pure echothiophate iodide (I), as crystalline form-SET; and    (3) echothiophate iodide (I) having assay by potentiometric titration method of 95-102 wt/wt.% and melting point of 106-114 degrees C (capillary method) and differential scanning calorimetry (DSC) isotherm having an endothermic peak of 122-128 degrees C.    DESCRIPTION OF DRAWING(S) - The drawing is a graph of X-ray powder diffraction pattern of crystalline echothiophate iodide (I) form-SET.