Abstract: In order to promote the accuracy of test results, the uncertainties in measurement of chromium (Cr), nickel (Ni), arsenic (As), selenium (Se), cadmium (Cd), and lead (Pb) in tobacco samples by inductively coupled plasma mass spectrometry (ICP-MS) were evaluated according to JJF 1059.1-2012 Evaluation and expression of uncertainty in measurement. The factors affecting the uncertainty were analyzed systematically with a cause-and-effect diagram, a procedure for assessing the uncertainty in the measurement was then developed, and the uncertainty of individual component was estimated with mathematic models. The results showed that: 1 ) The determined values for Cr, Ni, As, Se, Cd, and Pb were 1.41, 3.26, 0.42, 0.69, 1.97 and 4.11 μg/g, respectively; their expanded uncertainties at a confidence level of 95% were 0.10, 0.21, 0.03, 0.10, 0.13, and 0.33 μg/g, respectively. 2) The major factors influencing measurement uncertainty included recovery, repeatability, calibration curve fitting, and standard solution preparation. 3) The precision and accuracy of test results could be improved by preparing standard solution with gravimetric method, choosing a proper concentration range for standard working solution, and ensuring the stability of instrument by minimizing drift.