Abstract: OBJECTIVE To evaluate for the uncertainty of the concentration of (C₆H₅)₄BNa (0.02 mol·L^-1) titration solution prepared and calibrated according to the method in the Chinese Pharmacopoeia first addition of the 2010 edition. METHODS According to the sources of uncertainty analysis, the measurement model was established and the various influencing factors in the calibration process was evaluated. RESULTS By calculating each fraction of uncertainty in various variable parameters, the relative standard uncertainty was 4.46×10^-3, the combined uncertainty was 8.9×10^-5, and the expanded uncertainty was 0.000 18 mol·L^-1, k=2. CONCLUSION The method of the uncertainty evaluation for calibrating the concentration of (C₆H₅)₄BNa titration solution is established. The more reliable results of the measurement could be obtained when the measure was optimized by magnitude analysis all uncertainty.