The dependence of exchange anisotropy of polycrystalline Mn3IrCo70Fe30 bilayers on the antiferromagnetic layer thickness (dAF) was investigated. The degree of order of a Mn-Ir layer in the examined bilayers was almost constant of 0.45, regardless of dAF. The findings are stated as follows. A maximum unidirectional anisotropy constant (JK) of 1.3 ergcm2 is obtained at dAF=10 nm. The critical thickness of dAF, where JK becomes half of its maximum value, is less than 5 nm and comparable to that of the bilayer with disordered Mn-Ir. The blocking temperature (TB) is enhanced in several-ten degrees with ordering of the Mn-Ir layer.