An experimental study of convective boiling heat transfer of water flowing in minichannels at low flow rate is carried out with pure de-ionised water and copper-water nanofluids. A low concentration of copper nanometer-sized particles was used to enhance the boiling heat transfer. The aim is to characterize the surface temperature as well as to estimate the local heat transfer coefficients by using the inverse heat conduction problem IHCP. The inlet water temperature is fixed at 60°C and mass fluxes operated in range of 212-573 kg/m².s in minichannels of dimensions 500×2000 μm². The maximum heat flux investigated in the tests is limited to 7000 W/m². The results show that the surface temperature and the local heat transfer coefficient are dependent on the axial location and the adding of copper nanoparticles can significantly improve the heat transfer.