The fast, sensitive and selective detection of some antibiotics and heavy metal cations in water is highly desirable for environmental protection and human health, but it is still currently challenging. In this work, a new luminescent Eu(III)-based metal-organic framework (MOF), {[(CH₃)₂NH₂][Eu(L)₂(H₂O)₂]·xDMF_n (1) [H₂L = 4,4’-((naphthalene-1,4-dicarbonyl)bis(azanediyl))dibenzoic acid], was solvothermally synthesized. Complex 1 exhibits good water stability and luminescent property and could serve as a bi-functional ratiometric luminescent sensor for fast, sensitive and selective detection of ornidazole (ODZ) and Hg²⁺ in aqueous solution. The corresponding luminescent mechanism has also been discussed. This work indicates that 1 as a promising luminescent material exhibits luminescent quenching behavior for ODZ and luminescent enhancement behavior for Hg²⁺ in H₂O, which will promote the practical application of Ln-MOF-based ratiometric luminescent sensors in monitoring antibiotics and metal ions pollutants in the environmental water matrices.