The direct measurement of 133Ba source activity by the application of the theoretical count rate equations has been recently developed by Novković et al. The analytical and Monte Carlo calculation of activity measurement uncertainties were described in previously published papers for the case of one recorded spectra. The procedure of uncertainty calculation for a sequence of successively recorded spectra, enabling the determination of the correlation between peak count rates, is presented in this paper. The uncertainty of activity obtained by the described method is caused by the uncertainty of the experimentally obtained input data and uncertainties of the used nuclear decay data.