A nanofluid, which we used as a heat transfer fluid involving a suspension of nanoparticles in the colloid phase, was prepared from silver sitrate (precursor), ethylene glycol (reducing agent), and Poly(acryl-amide-co-acrylic acid) (dispersion stabilizer). The size and distribution of the silver particles were investigated with respect to the different amounts of dispersion stabilizer. in addition, different concentrations of the silver nanofluid (1000~10000 ppm) were prepared to investigate the potential improvement in thermal conductivity. The silver particle size became smaller, and the degree of particle distribution became correspondingly narrower, upon increasing the amount of dispersion stabilizer. Typically, the average particle size was about 10 nm when the PAA-co-AA/AgNO3 ratio was greater than . Thermal conductivity improved by 10, 16, and 18% as the concentration of silver particles in the nanofluid increased to 1000, 5000, and 10000 ppm, respectively.