In view of recent measurements of the mixing angle theta_13, we investigate the possibility to determine the difference of two CP Majorana phases of the neutrino mixing matrix from the study of neutrinoless double-beta decay.We show that if cosmological measurements will reach the sensitivity of 0.1 eV for the sum of neutrino masses, i.e., the mass value of the lightest neutrino will be strongly constrained, the long-baseline neutrino oscillation experiments will determine inverted hierarchy of neutrino masses and if neutrinoless double-beta decay will be observed, this determination might be possible. The required experimental accuracies and the uncertainties in the calculated nuclear matrix elements of the process are discussed in this context.