Abstract: In order to analyze the stability and thermal conductivity of nanofluids, Al ₂O ₃ nanofluids based on DI-water and EG were prepared by a two-step method, and different dispersant were added to avoid particle aggregation. The UV/VIS Spectrophotometer and Hot Disk thermal constant analyzer were used. The results reveal that absorbance can appraise the stability of nanofluids effectively, but the influence of dispersant should be considered. Ultrasonic oscillations can destroy the accumulation of nanoparticles, and it is 1h for the best effect. Moreover, dispersant, particle volume fraction, temperature and based fluids are all the influencing factors on thermal conductivity of nanofluids. When the temperature is 50℃, the thermal conductivity of 0.5% Al ₂O ₃-water nanofluids with 0.2% PVP has been improved by about 20%. Nanofluids can enhance the thermal conductivity of working fluids effectively, and the heat transfer performance of system can also be improved.