This study was concerned with the development of a heavy duty rust-converting agent, the function of which is to form metal complex coatings, containing vinyl halide-acrylic terpolymer emulsion, defoamer, emulsifying agent, glass flakes, chelating agent such as gallotannic acid, gallic acid, and pyrogallic acid, and other additives. The resulted emulson products(Sample No. 1∼No. 5) were characterized through test either in the forms of emulsions, which include Viscosity, Veneration rate, Acidity and Film drying rate test, or in the forms of coated layer on rusty steel substrates by FT-IR, which include hardness, gloss, salt spray, adhesion and flame retardant test. The test results are as follows ; Peneration rate(0.1∼0.4 ㎜/min), Soild content(70%), Acidity (pH 1.8∼2.0), Specific gravity(1.30∼1.35), Film drying rate(108min, RH 40%; 150min, RH 80%), Gloss(83∼92, incident angle 60˚; 88∼97, incident angle 85˚), Pencil hardness(4H∼5H), Adhesion (100/100), Salt spray test($gt;720Hr), LOI(%) value(38%), Vertical burning test(UL 94-v-1). According to the various performance of specimens show above, the evaluation of the availability of this heavy duty rust-converting agent can be concluded that all the samples(No. 1∼No. 5) are capable of being used in the field of chemical plant and in the hazard areas of fire and explosion potential. It was observed that the properties of sample No. 2, especially gloss and hardness, were much better than that of the other samples.