The first double-walled bimetal-organic framework [Cd4K4(TADA)(4)(H2O)(12)]center dot 6DMF (1, TADA = 3,3'-((6-hydroxy-1,3,5-triazine-2,4-diyObis(azanediyl)) dibenzoate) has been successfully constructed. In virtue of its high porosity and abundant basic sites, MOF 1 can be served as a high-efficiently size-selective heterogeneous catalyst for Knovenagel condensation reaction. Remarkably, 1 also exhibits excellent luminescent detectability for metronidazole (MDZ) with the highest quenching constant (K-sv) of 1.16 X 10(5) M-1. The results demonstrate that 1 can be served as a unique bifunctional platform for antibiotics sensing and size-selective catalysis.