Asphalt emulsion is manufactured by emulsification of asphalt, and it is an energy-saving, ecologically safe material because it does not need any heating processes which can emit gas and fire hazard in its use. The purpose of this study is to elucidate the feasibility on using pre-vulcanized natural rubber latex as an admixture for asphalt emulsion in order to improve thermal stability and useful mechanical properties of the asphalt emulsion. The crosslink density was determined by swell ratio. The effect of vulcanizing agent on residue properties of modified asphalt emulsions was studied. The morphology properties of the modified asphalt were also investigated by using an optical microscope. The results showed that asphalt emulsion which was modified using pre-vulcanized NR latex could provide a standard asphalt emulsion and applicable for highway construction application. The mechanical and physical properties of the dried asphalt emulsion were also very well modified by the vulcanized rubber phase. The residue properties of modified asphalt with natural rubber and pre-vulcanized natural rubber latex, including softening point and penetration was improved. The increase in vulcanizing agent could also increase softening point. At low polymer contents, the samples reveal the existence of dispersed polymer particles in a continuous bitumen phase, whereas at high polymer contents a continuous polymer phase was observed.