Assertive relationships are those in which the underlying attitude is one of “I’m OK: You’re OK” –there is mutual respect and regard, a curiosity about differences, and a willingness to work together in overcoming setbacks. In such organizations, people feel that they matter, others matter and that everyone is part of achieving business success through engagement with each other and with what they are doing. Especially in this type of organization leadership style represent an important factor that affectsthe enhancement of organizational performance and employee’s job performance, and what objectives they should pursue. Literature reviews on transformational leadership show its positive association with performance outcomes, particularly in private companies. A great deal of research has examined the significant impact of transformational leadership on work outcomes such as work performance and employee reactions and demonstrated that leaders who adopt the transformational leadership approach are better able to motivate employees to perform beyond expectations. The current research aims at exploring the relationship between assertiveness and employee job performance (task and contextual), additionally examining the mediating effect of transformational leadership.The study is based on a cross-sectional design, data is collected from 138 employees through the following structured questionnaires: MLQ –Multifactor Leadership Questionnaire, Job Performance Scale, and Rathus Assertiveness Schedule.The results of the study suggest that assertiveness positively predicts job performance. Particularly, the study also finds that transformational leadership significantly mediated the effect of transformational leadership on job performance. Specifically, the findings revealed a positive and significant relationship between assertiveness and both job performance and transformational leadership, as well as the fact assertiveness through transformational leadership, fosters job performance.Based on these findings, it canbe observed that assertiveness, job performance, and transformational leadership are important elements that can improve organizational performance. The practical implications of the recent study are discussed as well as some directions for future research in the area.