A flow calorimeter was developed to measure the isobaric heat capacities of pure water at high pressure and high temperature up to supercritical region. Experimental isobaric heat capacities of pure water from 395 K to 665 K and pressure up to 26 MPa are presented. The total measurement uncertainties of temperature and pressure were +/- 0.02 K and +/- 3.88 kPa, respectively. The relative uncertainty of the isobaric heat capacity was estimated to be +/- 0.98%. The aim of this study is to provide new experimental data to complete the non-experimental data region and to check the accuracy of the IAPWS-95 formulation. The IAPWS-95 formulation shows great accuracy at temperatures under 623 K and at pressures under 22 MPa region. However, in the near-critical and supercritical region, its accuracy needs more experimental data for verification and to extend theories. (C) 2015 Elsevier B.V. All rights reserved.