Abstract: The standard solution of sodium thiosulfate adopted in Chinese Pharmacopoeia 1953 leads to an error up to 1.2 psT cant when standardized against neutral iodine solution. The error is minimized to 0.5-0.6 per cent when the iodine solution is prepared according to the pharmacopoeial direction. It may be completely eliminated by adding 5mls. of 0.1N HC1 just before titration. The standardization of sodium thiosulfate solution against potassium dichromate is modified as follows: Place about 30-40mls. of 0.1 N K₂Cr₂O₇ solution, accurately measured with a burette, in an iodine flask. Dilute with 50mls. of water. Add 20mls. of 15 per cent potassium iodide solution, then about 5.3mls. of 6 N HC1. This is titrated immediately with Na₂S₂O₃ solution, using starch solution as indicator.