Enhancement of ultraviolet absorption through localized surface plasmon resonance (LSPR) was realized by assembling of Pd nanoparticles on homoepitaxial diamond thin films. The result of UV-vis spectrum of Pd nanoparticles embedded in diamond surface demonstrated the LSPR at wavelength of 213 nm, resulting in the improvement of ultraviolet absorption in diamond. The diamond ultraviolet photodetectors with and without Pd nanoparticles were fabricated and investigated. The results showed that the photoresponse from photodetector with Pd nanoparticles was 57.28 mA/W under 210 nm light at 5 V, which was three orders higher than that of detector without nanoparticles, and the UV/viable rejection ratio can reach to 4 orders of magnitude. This excellent performance should be attributed to LSPR in Pd nanoparticles, which was further confirmed by finite difference time domain (FDTD) simulation.