Abstract: The uncertainty semimicro-Kjeldahl method of measurement results for the was evaluated in this example. determination of total The results show that nitrogen in soil samples by the main sources of the total uncertainty comes from the fraction uncertainties of weighting of borax standard and sample, purity of borax, volume of volumetric flask, pipette and burette, molar mass of relative elements and measurement repeatability. The total uncertainty for the determinations of total nitrogen by semimicro-Kjeldahl method was combined and its extended uncertainty was obtained via multiplying it by extended factor of 2 under confidence probability of 95%.