High dielectric loss is the main factor that leads to easy aging and low service reliability of electronic and insulation products. Herein, novel heat and moisture-resistant bismaleimide (BD) resins with ultralow dielectric loss and high toughness were developed through synthesizing unique amino-functionalized metal-organic framework (sN-MIL) with small pore diameter and low specific surface. The addition of only 0.3 wt% sN-MIL into BD resin effectively improves impact strength and fracture toughness to about 1.70 times; meanwhile significantly reducing dielectric loss to only 0.0004 (100 Hz), which is almost the lowest dielectric loss reported among porous filler/polymer composites. The origin behind these attractive performances of sN-MIL/BD composites was intensively discussed.