Self-knowledge has been defined as the accurate self-perceptions about how one typically thinks, feels, and behaves, and awareness of how those patterns are interpreted by others. Previous research has noted that the introspection and the reflected appraisal processes are two main avenues for learning about the self and that self-knowledge might be fully realized through the use of reflected appraisal from close others. However, due to the methodological difficulty in linking people's ratings on a trait to their behaviors, accuracy research using a behavioral criterion is quite limited. The current work examined the main source of learning about one's self-knowledge by investigating the time course of attention deployment both in the process of introspection and that of reflected appraisal. Twenty-five college students were first asked to rate their impressions of their classmates as well as a familiar other using personality-trait adjectives. Their electrophysiological data were then collected using the event-related potential (ERP) technology while they judged to which extent (1) an adjective can describe the self, (2) an adjective can describe a familiar other, (3) they agree with an adjective that their classmates believe can describe the self, and (4) they agree with an adjective that their classmates believe can describe a familiar other. Our electrophysiological data showed that classmates’ positive evaluation of one's own trait elicited larger P2 than the positive self-evaluation of one's own trait. Further, classmates’ negative evaluation of one's own trait elicited larger late positive component (LPC) than the negative self-evaluation of one's own trait. Results suggest that people allocate more attention to the process of reflected appraisal compared to the process of introspection, which further suggests that the reflected appraisal process might be the main source in learning about one's self-knowledge of personality.