We characterize probability measure with finite moment of any order in terms of the symmetric difference operators of their Fourier transforms. By using our new characterization, we prove the continuitystands for the density of unique measure-valued solution (F t ) t≥0 of the Cauchy problem for the homogeneous non-cutoff Boltzmann equation, with Maxwellian molecules, corresponding to a probability measure initial datum F 0 satisfying |v| 2k−2+α dF 0 (v) < ∞, 0 ≤ α < 2, k = 2, 3, 4, · · · , provided that F 0 is not a single Dirac mass.MSC: Primary 35Q20, 76P05; secondary 35H20, 82B40, 82C40