In the crystal structure of the title compound, C(4)H(8)N(2)O(4)·C(18)H(15)OP, two triphenyl-phosphine oxide mol-ecules and two dimethyl hydrazine-1,2-dicarboxyl-ate mol-ecules are connected via N-H⋯O hydrogen bonds of moderate strength and are related via a twofold rotational axis. Weak C(ar)-H⋯ O contacts strengthen the crystal structure.