Assuming positive observation of neutrinoless double bata decay together with the CHOOZ reactor bound, we derive constraints imposed on neutrino mixing parameters, the solar mixing angle θ 1 2 and the observable mass parameter <m> β in single beta decay experiments. We show that 0.05 eV =<<m> β =< 2 eV at the best fit parameters of the LMA MSW solar neutrino solution by requiring the range of the parameter <m> β β deduced from recently announced double beta decay events at 95% CL with +/-50% uncertainty of nuclear matrix elements.