In this work, thermophysical properties, microstructure, and pool boiling characteristics of water-in-polyalphaolefin (PAO) nanoemulsion fluids have been measured in the water concentration range of 0–10.3 vol. %, in order to gain basic data for nanoemulsion boiling. Water-in-PAO nanoemulsion fluids are formed via self-assembly with surfactant: sodium sullfosuccinate (AOT). Thermal conductivity of these fluids is found to increase monotonically with water concentration, as expected from the Maxwell equation. Unlike thermal conductivity, their dynamic viscosity first increases with water concentration, reaches a maximum at 5.3 vol. %, and then decreases. The observed maximum viscosity could be attributed to the attractive forces among water droplets. The microstructures of the water-in-PAO nanoemulsion fluids are measured via the small-angle neutron scattering (SANS) technique, which shows a transition from sphere to elongated cylinder when the water concentration increases above 5.3 vol. %. The pool boiling heat transfer of these water-in-PAO nanoemulsion fluids is measured on a horizontal Pt wire at room temperature (25 °C, subcooled condition). One interesting phenomenon observed is that the pool boiling follows two different curves randomly when the water concentration is in the range of 5.3 vol. % to 7.8 vol. %.