As a promising processing technique for machining hard and brittle materials, ultrasonic-assisted grinding (UAG) has been extensively employed in manufacturing industries. To determine the material removal mechanism in the UAG of SiC ceramics, the deformation features of SiC ceramics in ultrasonic-assisted scratching (UAS) tests were compared with those in conventional scratching (CS) tests using a combination of simulations and experimental observations. The results indicated that the scratching groove formed in the CS process appears straight, while it is sinusoidal in the UAS process. There are two scratching modes in the UAS process: an intermittent mode and a continuous mode. The critical depth of cut in UAS is deeper than that in CS. This study confirmed that UAG is a highly effective processing method for machining hard and brittle materials.