Abstract: In order to determine a certain kind of effective inhibitor adopted in reverse flotation process of a limonite mine in Xinjiang，the optimum test on the inhibitor of reverse flotation were carried out. The inhibition mechanism of the inhibitor was studied through surveying the surface ζ potentials of limonite under the condition of three different types of amyloid inhibitor. The results indicated that:①Under acidic conditions，the inhibit effect of iron is weakened orderly from sodium carboxymethyl starch，soluble starch to tertiary ammonium cationic starch. Under alkaline conditions，the inhibit effect of iron will be declined from tertiary ammonium cationic starch，soluble starch to sodium carboxymethyl starch. ②Taking sodium carboxymethyl starch with best inhibiting effect as inhibitor，iron ore concentrate with grade of 60.79% and recovery of 79.96% was obtained by adopting the process of one-roughing，two-cleaning，one scavenging and middles back to the flow-sheet in turn. ③The limonite ore with positive surface charges absorbs much sodium carboxymethyl starch(anionic starch) under acidic condition，which is the reason for the excellent inhibit effect on iron in acidic environment; The limonite ore with negative surface charges absorbs much tertiary ammonium cationic starch under alkaline condition，which is the reason for excellent inhibit effect on iron in alkaline environment.

Key words: Limonite, Reverse flotation, Sodium carboxymethyl starch, Soluble starch, Tertiary ammonium cationic starch, Inhibitor, Potential