Abstract: Surface tension is one of the most important basic properties of liquid. Accurate measurement of surface tension plays an important role in industrial production and scientific research. At present, calibration of surface tensiometers in China lacks foundation due to the lack of detailed research on evaluation of measurement uncertainty of surface tension. This paper studies the measurement uncertainty in the error of indication of surface tensiometers based on the platinum plate method and the platinum ring method. The results showed that the main uncertainty components come from the measurement repeatability and the reference value. The uncertainty of reference value mainly comes from the probe size. The uncertainty caused by the special weights and the gravity acceleration is less than that caused by the probe size. For the same level of measurement repeatability, the uncertainty in the error of indication of a surface tensiometer based on the platinum plate method is greater than that of a surface tensiometer based on the platinum ring method.