Abstract: OBJECTIVE To establish a method for the evaluation of the uncertainty of the content determination of metformin hydrochloride in metformin hydrochloride tablets by UV. METHODS The model for evaluation of the uncertainty was established in measurement were analyzed. The influencing factors on the uncertainty in the procedure of the content determination were evaluated, including repeatability of results of measurements, the weight of sample, the dilated volume of sample, the measurement by ultraviolet visible absorption spectroscopy. RESULTS The expanded uncertainty U95 was 2.7%, the coverage factor was 2. CONCLUSION To make the measurement under control, the more reliable results of the measurement could be obtained when the measure was optimized by magnitude analysis all standard uncertainty.