Ultrasonic Vibration Assisted (UVA) machining is being used for direct diamond turning of hard-brittle materials to obtain optical-quality surfaces. It largely reduces the processing time and cost to produce the high accuracy surface on hard-brittle materials. However, our understanding of the cutting mechanics and surface generation in UVA diamond cutting of these materials is still far from complete. In this paper, an experimental investigation has been conducted to study the effect of the factors affecting the surface generation in UVA diamond cutting of hard-brittle materials. A series of tapered grooving experiments were conducted on optical glass (BK7), tungsten carbride (WC), and Silicon Carbide (RB-SiC). The factors under control in this investigation included vibration amplitude of the UVA system, cutting speed, cooling conditions and depth of cut. With appropriate selection of cutting parameters, the experimental results show that it is technically feasible to achieve ductile cutting of hard-brittle materials by UVA diamond cutting. The results provide an important means for better understanding the cutting mechanics and surface generation of UVA diamond cutting of hard-brittle materials.