In general, the prepackaged-type polymer-modified mortar products are made using copolymer powders or terpolymer powders. The products of polymer-modified mortars with the former are made considerably clear as popular construction materials. While those of the polymer-modified mortars with the latter are hardly clarified owing to a relatively short history of their use. Nowadays, various redispersible polymer powders have been commercialized to manufacture construction materials in the form of prepackaged-type products, which have rapidly been developed for lack of skilled workmen in construction sites. In recent years, the terpolymer powders of improved quality have been developed and commercialized as cement modifiers. However, the properties of polymer-modified mortars using terpolymer powders have not been studied till now. The purpose of this study is to evaluate the quality of polymer-modified mortars using a VA/E/MMA powder in comparison with polymer-modified mortars using VAE-1 and VAE-2 powders. Polymer-modified mortars using commercial terpolymer powders and a SBR latex as controls are prepared with various polymer-cement ratios, and tested for strengths, water absorption, chloride ion penetration, and carbonation. On the whole, the properties of VA/E/MMA terpolymer powder-modified mortars are considerably higher than those of VAE copolymer powder-modified mortars, and are remarkably improved over unmodified mortar. It is concluded from the test results that the modification of cement mortar with the VA/E/MMA terpolymer powder causes marked improvements in its properties like the SBR latex.