Food additives are usually added to improve food quality. But banned substance are often found e.g potassium bromate. Therefore we need a reagent to analyze the presence of potassium bromate and the reagent will be used to make a strip test for practical uses in detection potassium bromate. In this study, optimization of Ag nanoparticles volume and acid red 14 concentration has been done. Acid Red 14 was oxidized to colorless in the presence of potassium bromate. Result showed that each 25 mL reagent consist of 10 mL Ag nanopaticles; 0,002 mM acid red 14; and 1 mL 0,2 M H2SO4.