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The HO content of wadsleyite were measured in a wide pressure (13-20 GPa) and temperature range (1,200-1,900°C) using FTIR method. We confirmed significant decrease of the HO content of wadsleyite with increasing temperature and reported first systematic data for temperature interval of 1,400-1,900°C. Wadsleyite contains 0.37-0.55 wt% HO at 1,600°C, which may be close to its water storage capacity along average mantle geotherm in the transition zone. Accordingly, water storage capacity of the average mantle in the transition zone may be estimated as 0.2-0.3 wt% HO. The HO contents of wadsleyite at 1,800-1,900°C are 0.22-0.39 wt%, indicating that it can store significant amount of water even under the hot mantle environments. Temperature dependence of the HO content of wadsleyite can be described by exponential equation $$ C_{{{\text{H}}_{2} {\text{O}}}} = 6 3 7.0 7 {\text{e}}^{ - 0.00 4 8T} , $$ where T is in °C. This equation is valid for temperature range 1,200-2,100°C with the coefficient of determination R = 0.954. Temperature dependence of HO partition coefficient between wadsleyite and forsterite ( D) is complex. According to our data apparent D decreases with increasing temperature from D = 4-5 at 1,200°C, reaches a minimum of D = 2.0 at 1,400-1,500°C, and then again increases to D = 4-6 at 1,700-1,900°C. [ABSTRACT FROM AUTHOR]