Deoxyribonucleic acid (DNA), as one kind of biopolymer, has recently emerged as an attractive optical material, showing promise in making versatile optoelectronic devices. In the present study, we report the fabrication and characterization of DNA biopolymer nanocomposite with tunable conductivities and the application in bistable memory device. DNA nanocomposite consisting of DNA biopolymer and silver nanoparticles is synthesized using a phototriggered method. The nanocomposite exhibits tunable conductivities when exposed to UV light under different periods of time. The electrical conductivity is suggested to be dependent on the quantity and the distribution of silver nanoparticles formed in DNA biopolymer. In addition, a memory device based on DNA biopolymer nanocomposite is demonstrated. The operation of different conductivity states can be adjusted by the concentration of nanoparticles. The device shows bistability of current, and presents a stable write-read-erase cycle. Detailed performance of the DNA-based memory device will be presented and discussed.