The standard ISO/IEC 17025:2005 on the competence of testing and calibration laboratories requires that these laboratories shall apply procedures for estimating the uncertainty of their measurement results. One of the possibility is to evaluate the budget of uncertainty, taking into account all components that contribute significant uncertainty to the final result. In case of the sound absorption coefficient measurement, carried out according to the standard EN ISO 354:2003, the overall uncertainty is first of all influenced by the reverberation times T1, T2 and the power attenuation coefficients m1 and m2, calculated according to the ISO 9613-1 standard and representing the climatic conditions in the reverberation room. In spite of very little difference between the values m1 and m2 representing the change of climatic conditions (usually, it is the case in laboratory), exponential form of the coefficient's function causes that the uncertainty of measurement results increase with frequency very fast. Particularly for the high frequencies, the values of uncertainty are so important that the evaluation of the sound absorption coefficient is practically not possible.