In order to evaluate influence of water on the pressure and transition interval of the olivine-wadsleyite transition, synthesis experiments were carried out in hydrous Forsterite90 composition at 9-16 GPa and 1273-1873 K. Three additional starting materials, representing (a) Mg 2SiO4, (b) San-Carlos olivine (Fo89) and (c) CaO-MgO-Al2O3-FeO-SiO2 peridotite, were loaded in every experimental assembly simultaneously. We observed significant expansion of olivine + wadsleyite stability loop to the lower pressure for 2-3 GPa at 1473 K, whereas there was no significant shift of the phase transition boundary at 1873 K. These results are consistent with thermodynamic calculations made by Wood and inconsistent with recent experimental data by Chen et al. We report here preliminary results on water content of coexisting phases. Water solubility of olivine increases with pressure up to 0.15 wt.% H2O at 14 GPa. At 12-15 GPa H2O content of olivine is almost the same at temperatures from 1373 to 1773 K, whereas the H2O content of wadsleyite decreases from about 2.1 wt.% at 1373 K to 0.7 wt.% at 1773 K. We determined the partition coefficient of H2O between two phases. Dwd/ol is 11.8 at 1473 K, 7.2 at 1673 K and 4.5 at 1773 K. However if we apply recent calibration of H2O content in olivine by Bell et al. these Dwd/ol values are three times lower.