Abstract: Nano Ag-Ga alloy/Poly 2-acrylamide -2- methyl propane sulfonic acid(PAMPS) composite materials were prepared without emulsifier and reductant by ultrasonic irradiation emulsifier-free emulsion polymerization. XRD and FI-IR suggested that nano-Ag₃Ga particles are hexagonal crystal structure and there is interaction between gallium atom of alloy and carbonyl oxygen. HRTEM showed that nano-Ag₃Ga particles are homogeneously dispersed in polymer martrix, and the size of particles is 10-15nm and have effect of induced polymer orderly assembly.TG and DTG proved that nano-Ag₃Ga dispersion in the composite enhance the thermal stability of PAMPS.