Provided are an organometallic compound represented by Formula 1, an organic light-emitting device including the organometallic compound, and a diagnostic composition including the organometallic compound: M1(L11)n11(L12)n12  Formula 1 wherein L11 in Formula 1 is a ligand represented by Formula 1-1: wherein, in Formula 1-1, Ar1 is a phenyl group substituted with at least one of E1 and Ar2 is a phenyl group substituted with at least one E2, and the other substituents are described in the detailed description of the present specification.