In this work nano silver added to the biodegradable polylactic acid can be prepared by casting method at room temperature and thickness (120 μm) at different concentration of nano silver powder. Optical properties have been measured in the range of (300-800) nm. The electronic transition in pure polylactic acid (PLA) and PLA/Ag nanocomposites indicated direct allowed transition. Also, it is found that the energy gap of polylactic acid is 3.3 ev and this value decreased within range of (3.3-2.7) eV when the concentration of nano silver powder increased from (2, 4, and 6%) respectively. The optical constants which include the refractive index (n), real (ε1) and imagenerary (ε2) part of dielectric constant calculated at λ=550 nm and find it decreased with increasing of nano silver.