Objective: The objective of the present study is to examine the serum stability of siRNA loaded nanoparticles that were prepared with certain polymer and evaluate the influence of different pH values on the in vitro release of siRNA from these particles. Methods: Serum stability of siRNA loaded nanoparticles was studied by incubation in serum free medium and in presence of 10 %, and 25 % serum at 37ºC for 6 h. The unshielded fraction (liable to nucleases) of siRNA was measured by Fluoroskan microplate reader at l_ex = 485 nm, and l_em = 518 nm using fluorescence PicoGreen dye. The in vitro release of siRNA from nanoparticles, measured by electrophoresis, was studied in DMEM at two different pH values of 3.5 and 7.4. Results: The results of serum stability showed that 8.6 %, 24.4 %, and 23.5 % siRNA was unshielded from the nanoparticles in the presence of 0 %, 10 %, and 25 % serum, respectively. After 12 h, the released fraction of siRNA was 17.8 % and 95.2 % at pH 7.4 and pH 3.5, respectively. Conclusion: The obtained results revealed that the nanoparticles were considered as a reasonable delivery system that could protect siRNA from degradation by nucleases enzymes upon systemic injection and able to release the loaded siRNA in the acidic pH inside the required cells.