The wettability of the heated surface under pool boiling of surfactant solutions and nano-fluids has been investigated. Tri-sodium phosphate (TSP, Na3PO4) solutions (0.01, 0.05, 0.1, 0.3, 0.5, 0.8 wt.%) and Aluminum oxide (Al2O3) nano-fluids (NF) (0.5, 1, 2, 4 vol.%) were prepared for experiments. Stainless steel (SUS 304) strips (30 x 30 x 3 mm) were heated by an alcohol lamp and quenched in the prepared solutions. Before complete quenching, when the surface temperature was 150 +/- 10 degrees C (nucleate boiling region), the strip was taken out and excessive liquid on the surface was removed. Contact angles of pure water and the solutions oil the quenched surface and fresh surface were measured. Contact angles of pure water oil the quenched surfaces (5 degrees-25 degrees) were much smaller than those on the fresh surface (65 degrees-70 degrees). The solutions (TSP, NF) on the quenched surface shows the smallest contact angle (5 degrees-15 degrees). Surfaces deposited TSP and nano-particle could affect surface energy of the strips and enhance hydrophilicity of the surfaces. Several implications of the experimental results on the pool boiling CHF model and CHF enhancement using TSP and NF were discussed. (c) 2007 Elsevier Ltd. All rights reserved.