Abstract: An uncertainty evaluation method for Brinell hardness test was introduced, and those uncertainties associated with the hardness-reference block, hardness testing machine, and specimen were taken into account. In other words, the effects to the separated uncertainties were calculated to derive the expanded uncertainty. The testing results of 45 steel forging specimen were X=(185.0±3.6) HBW5/750, k=2, and the relevant deviation of hardness was 1.5%. The results show that the effect of uncertainties to the hardness test results was acceptable.