The present invention discloses a LPR sensing device and a LPR sensing system comprising a LPR sensing device, a light source, a detecting unit and a processing unit. The LPR sensing device comprises a sensing substrate and a noble metal nanoparticle layer, and the noble metal nanoparticle layer is disposed on the sensing substrate and has noble metal nanoparticles with diameter of 2˜12 nm. An analyte adsorbed on the surface of the noble metal nanoparticle layer generates a dielectric environmental change, resulting in a change of the LPR band. Comparing noble metal nanoparticles with different particle diameters, small noble metal nanoparticles provide better sensing sensitivity to a compound with a small molecular weight.