Abstract: Using high energy X-ray defocus phase contrast imaging on polystyrene(PS) microspheres, the contrast of the edge of tiny bubbles (about a few micrometers in diameter) in the sphere’s wall are effectively enhanced, where the density gradient is relatively larger, and thus the bubbles will be highlighted on the image of microsphere which has overall smooth gray scale. The contrast causing and related factors are analyzed and discussed. The experiments conducted use micro-focal spot X-ray tube and CCD as the light source and detector, the derived image resolution is better than 2 μm, and the rapid defect detection of PS shells is achieved at the X-ray energy of 20 to 30 keV, providing a fast and effectiving means for monitoring of microspheres preparation process.