A stability of nanofluids  makes an efficient heat transfer enhancement which is applicable in various area such as power generation, micro electronics, defense, space, electronic components cooling, nuclear, biomedicals and so on. The stability and durability of the nanofluids which concern the more thermal conductivity in most of the industrial applications. The preparation and stability of nanofluids are the two common kinds which is reports by this article. The two step method is use to prepare the nanofluids. The Al2o3 – Distilled water nanofluids with same concentration and different temperature are used in this experiment. Then the two step method is done by using the magnetic stirring and ultrasonic vibrations, the magnetic stirring time and ultra sonication time and temperature makes as efficient and good stability of the nanofluids. The stability of nanofluids is analysed by visual method.