Disclosed is a stainless steel for a separator of a polymer fuel cell having excellent corrosion resistance. More particularly, disclosed is a stainless steel for a separator of a polymer fuel cell having excellent corrosion resistance in a sulfuric acid environment which is a fuel cell operating environment. According to an embodiment, the stainless steel for a separator of a polymer fuel cell includes, in percent by weight (wt %), 0.09% or less of C, 1.0% or more and less than 2.5% of Si, 1.0% or less (excluding 0) of Mn, 0.003% or less of S, 20 to 23% of Cr, 9 to 13% of Ni, 1.0% or less (excluding 0) of W, 0.10 to 0.25% of N, and the remainder of Fe and other inevitable impurities, wherein a corrosion resistance index represented by Formula (1) below is 7 or more. 3 * ⁢ W + 1.5 * Si + 0.1 * Cr + 20 * ⁢ N - 2 * ⁢ Mn ( 1 ) In Formula (1), W, Si, Cr, N, and Mn represent the content (wt %) of each element.