The present invention relates to a write-once and read-many-times memory device and the fabricating method thereof. The structure of the memory device comprises: a substrate, a first electrode, a double helix biopolymer layer and a second electrode, and a plurality of metal nanoparticles are distributed in the double helix biopolymer layer. The first electrode is disposed on the substrate, the double helix biopolymer layer is disposed on the first electrode and the substrate, and the second electrode is disposed on the double helix biopolymer layer. When illuminating, the memory device will produce a low-conductivity state and high-conductivity state for writing data. Later, when a voltage is applied to the first electrode and the second electrode, the data will be read.