The present study examines the influence of raters’personality traits on the rating process of L2 argumentative writing and their interactions with argument positions. Four Korean EFL raters took a personality test and scored four essays composed by Korean EFL university students, thinking aloud their rating processes. The raters’decision-making behaviors were analyzed to investigate the role of their personality during the rating process. Results of the study reveal that the raters not only shared certain rating strategies due to the nature of scoring L2 argumentative essays but also illustrated personalityspecific variations in decision-making behaviors and this appeared to interact with the essay argument positions. A pair of raters, found to be extroverted perceivers, favored supporting argument and attempted to interpret the writer’s intention or correct linguistic errors with more emotional engagement with the writer; the other pair, the introverted judgers, preferred the counter-argument, and were highly goal-oriented and time conscious, scoring more objectively and efficiently with more foci on task completion and the quantitative aspects of writing. The raters also demonstrated variations within the pair group. The study suggests raters’personality traits can be a source of rater variation, which influences scoring validity and reliability of writing assessment.