Provided is a modified ethylene-vinyl alcohol copolymer, wherein the copolymer is represented by a following formula (I), contents (mol %) of a, b, and c based on the total monomer units satisfy following formulae (1) through (3), and a degree of saponification (DS) defined by a following formula (4) is not less than 90 mol %, 18≦a≦55  (1) 0.01≦c≦20  (2) [100−(a+c)]×0.9≦b≦[100−(a+c)]  (3) DS=[(Total Number of Moles of Hydrogen Atoms in X, Y, and Z)/(Total Number of Moles of X, Y, and Z)]×100  (4).