A simplified, sensitive , rapid and accurate spectrophotometric method was developed for the determination of Thiamine.HCl in pharmaceutical preparations and in pure form . The method is based on the reduced Fe(III) salt by Thiamine.HCl to form Fe(II) salt which subsequently react with potassium ferric cyanide forming a soluble Prussian blue dye which has a maximum absorption at λmax 747nm . Linear calibration graph was in the range of (0.2–14) µg.ml-1 with molar absorptivity of (2.42×103L.mol-1.cm-1) ,a sandall sensitivity of (139.38×10-6 µg.cm-2) , correlation coefficient of 0.9999 and the relative standard deviation of RSD%(0.617–0.362). The method was applied successfully for the determination of Thiamine,HCl in pharmaceutical preparations. Recovery was in the range of (97.8–104.4)%. The proposed method can be carried out at 40°C temperature with no need for solvent extraction step or pH control.