The η-η′ pseudoscalar mixing angle and the gluonium content of the η′ meson are deduced from an updated phenomenological analysis of J/ψ decays into a vector and a pseudoscalar meson. In absence of gluonium, the value of the mixing angle in the quark-flavor basis is found to be φP=(40.7±2.3)°. In presence of gluonium, the values for the mixing angle and the gluonic content of the η′ wave function are φP=(44.6±4.4)° and Z2 = 0.29-0.26+0.18 respectively. The newly reported values of B(J/ψ→ρπ) by the BABAR and BES Collaborations are crucial to get a consistent description of the data. © Springer-Verlag / Società Italiana di Fisica 2009.