Background: It has recently been shown that the particle size of materials used for radiation shielding can affect the magnitude of radiation attenuation. Over the past years, application of nano-structured materials in radiation shielding has attracted attention world-wide. The purpose of this study was to investigate the shielding properties of the lead-free shields containing micro and nano-sized WO3 against low energy x-rays. Materials and Methods: The radiation shields were constructed using nano and micro WO3 particles incorporated into an EPVC polymer matrix. The attenuation coefficients of the designed shields were evaluated for low energy x-rays (diagnostic radiology energy range). Results: The results indicate that nano-structured WO3/PVC shields have higher photon attenuation properties compared to those of the micro-sized samples. Conclusion: Our experiment clearly shows that the smaller size of nano-structured WO3 particles can guarantee a better radiation shielding property. However, it is too early to draw any conclusion on the possible mechanisms of enhanced attenuation of nano-sized WO3 particles.