An experimental study has been conducted to examine the effect of different concentrations of α-Al 2 O 3 nanofluids on boiling heat transfer for downward facing heating. The experimental results indicated that the surface heat transfer was enhanced with the rise of the nanofluids concentration, due to the bubble generation rate and disturbance increased. For downward facing heating, bubbles were not able to escape since the bouncy force influenced, and the vapor film appeared earlier as the increase of bubble generation rate. However, the heat transfer coefficient remains at a relatively high value in the early stage of film boiling, which suppresses the deterioration of heat transfer, due to the influences of nanofluids. As the various concentrations of nanofluids increased from 0 g/L to 0.012 g/L, it was found that the enhancement of the CHF (critical heat flux) up to 20.5%. After the nanofluids boiling, the surface roughness decreased and the wettability became worse. From the experimental phenomena, under the influence of these two factors, the bubble activity was enhanced.