As a result of increased concerns regarding public safety in recent years, the impact and penetration resistance of infrastructure has become an emerging research focus in the cement and concrete industry. Ultra-high performance concretes (UHPCs) with fiber reinforcement usually possess compressive strengths greater than 200 MPa and are promising candidates for penetration-resistant building materials. In the current project, two UHPC materials, ERDC-M (a modified composition developed at U.S. Army Engineer Research and Development Center) and Ductal®, were subjected to projectile penetration testing. The microstructural evolution due to projectile impact and penetration was examined via scanning electron microscopy and X-ray diffraction. Possible phase changes were observed in the affected material volume, which can be interpreted as resulting from the high temperature and high pressure induced by the impact and penetration.