Repetition priming has been proved to be a potential tool for studying different stages in perceptual/cognitive processing. The human visual system efficiently allocates perceptual inputs to certain object categories (object categorization) and distinguishes among objects with similar visual features (object discrimination). These are two generally distinct but mutually complementary processes for visual object processing, whose temporal profiles can be elucidated by studying different types of repetition priming using event-related potentials (ERP) analyses. In this study, using an immediate repetition priming paradigm (prime and probe stimuli are presented consecutively without any intervening distracters), we compared the priming-triggered neural activities in face versus building processing. Two types of repetition priming were included: category repetition priming (prime and probe stimuli are different exemplars from a same object category) and item repetition priming (prime and probe stimuli are identical). Category repetition priming was employed to provide evidence for object categorization, and item repetition priming for object discrimination. Sixteen subjects were asked to respond as fast and accurately as possible to decide, with mouse clicks, whether the probe stimulus was a face (face trial) or a building (building trial), but to ignore the prime stimulus. During the task, their behavioral performance [reaction times (RTs) & error rates] and EEG were recorded simultaneously. The RT data showed significant category repetition priming effect in both face and building trials, but significant item repetition priming effect only in face trials. With respect to the ERPs, in face trials, a category repetition priming effect emerged at the N170 stage, and an item repetition priming effect at the P200 stage. In contrast, in building trials, repetition priming effects occurred already at the P100 stage. Our results, using repetition priming, provided evidence for different mechanisms underlying face and building processing.