Recent firm- and job- related trends which translate into flatter organizational structure and more complex and collective tasks have enhanced coworker’s salience and their potential influence. In this change, coworker’s interpersonal helping behaviors are considered as important factor to influence on fellow employee’s attitudes and behaviors. In general, it has been argued that coworker’s interpersonal helping behaviors positively affect fellow employee’s attitudes and behaviors. However, recent literatures suggest that, consequences of interpersonal helping behaviors will be different according as how the intention of helping behaviors is interpreted by rater. Moreover, helping behaviors significantly affect task performance rating because these behaviors are frequently emphasized as like in-role behaviors in organization. Therefore,why coworker’s helping behaviors are subjectively interpreted has to be investigated before we discuss about consequences of coworker’s interpersonal helping behaviors. Specifically,characteristics of help giver (actor) and receiver (rater) have to be considered simultaneously for understanding rating process of interpersonal helping behaviors in dyadic coworker relationship. The purposes of this study are to explain the cognitive process involved in rating of interpersonal helping behaviors and to demonstrate the influence of actor’s and rater’s trait on rating process concerning helping behaviors. We investigated moderate effects of two variables; ability to modify self-presentation as an actor’s trait and self-enhancement motives as a rater’s trait on the relationship between coworker’s helping behaviors and coworker’s OCB-I rated by fellow employee. Hypotheses are like these. H 1: Help giver’s ability to modify self-presentation will moderate the relationship between actor’s help giving and the extent of actor’s OCB-I rated by help receiver. That is,the positive slope will become smaller in graph when ability to self-presentation is high than when ability to self-presentation is low. H 2: Help receiver’s self-enhancement motives will moderate the relationship between actor’s help giving and the extent of actor’s OCB-I rated by help receiver. That is, the positive slope will become smaller in graph when self-enhancement motives is high than when self-enhancement motives is low. We conducted empirical test for examining hypotheses. Data were collected using questionnaires from 150 dyads of an employee and his/her coworker. As the result of the hierarchical regression analyses for OCB-I, the moderate effects of ability to modify self-presentation and selfenhancement motives on the relationship between coworker’s help giving and coworker’s OCB-I perceived by employee were significant respectively (ability to modify self-presentation: β =-.17, p < .05, self-enhancement motives: β = -.14, p < .05 ). Therefore, these results provided supports for Hypothesis 1, and 2. Our study demonstrated that coworker’s interpersonal helping behaviors were easily rated as OCB-I by raters when help giver was high in ability to modify self-presentation. This result provides important practical implication. Recently coworker’s supportive attitudes are emphasized as important factor to enhance organizational effectiveness. Therefore, coworker’s engaging in interpersonal helping behaviors are rated positively by fellow employees and positively influence on overall evaluation concerning actor. By the result of our study,however, helping behaviors of individuals high in ability to self-presentation have to be carefully evaluated in that individuals with high ability to self-presentation were better judged as compared with behaviors which they really engaged in. Our study proved that rater high in self-enhancement motives had a weak tendency to evaluate coworker’s helping behaviors as OCB-I. This result indicates that cognitive schema that rater brings to the evaluation process influences the rating of coworker’s interpersonal helping behaviors. Finally, our research contributes in providing understanding concerning employee’s interpretation of coworker’s helping behaviors. Nowadays coworker’s rating concerning fellow employee’s engaging in helping behaviors toward other employees is functioned as substantial control system in team based organizational structure. For instance, multi-source appraisal system including coworker rating is conducted by many firms. The results of our study suggest that training and rating criteria for accurate evaluation concerning coworker’s helping behaviors are needed to diminish rating errors.