Abstract: This paper aims to investigate how nanometer materials improve boiling heat transfer characteristics through a pool boiling experiment from a downward-facing surface at atmosphere pressure. Under inclined angle 0°, 15° and 30°, several pool boiling experiments were conducted in deionized water and different nanofluids. Visualization of boiling phenomena and bubble movement were recorded by utilizing a high-speed digital camera. Compared with deionized water, boiling heat transfer coefficient increases by 23.1% for Al₂O₃ nanofluids, 42.5% for Cu-20 nanofluids and 92.9% for Cu-100 nanofluids. It is found that boiling heat transfer coefficient increases with the volume concentration for Cu-20 nanofluids.