Provided are: a Mn+-exchanged beta zeolite which is useful for the catalytic removal of nitrogen monoxide contained in a gas to be purified even when oxygen is contained in the gas at a high concentration or when the gas has a low temperature; and a method for producing the Mn+-exchanged beta zeolite. The Mn+-exchanged beta zeolite according to the present invention has a SiO2/Al2O3 ratio of 7 to 18, and is ion-exchanged by a Mn+ ion (wherein Mn+ represents a n-valent metal cation; n represents a numeral value of 1 to 3; and M represents an element selected from the group consisting of Ni, Co, Cu, Mn, Zn, Sn, Ag, Li, K, Cs, Au, Ca, Mg, Pt, Pd, Rh and Ir). The amount of the Mn+ ion carried on the Mn+-exchanged beta zeolite is preferably from 0.01 to 2.5 mmol/g relative to the amount of the Mn+-exchanged beta zeolite.