Today, most organizations, if not all, used team-based work structures to organize its employees. Researchers and entrepreneurs focused on the issue that how to cultivate organizational resources to build effective work teams to improve organizational performance. Recently, the value of a supportive organizational climate had been recognized. However, there were little researches about its relationship with employees’ attitudes and behavior in work team-based organizational context. The purpose of this article is to explore how supervisor career supports influence on their direct followers’ organizational citizenship behavior under work team-based organizational structure. Sixty-six work teams (totally 303 work team members) were sampled from a large State-owned enterprise in a province from eastern China. Work team members completed a questionnaire consisting of supervisor career support, psychological capital and organizational citizenship behavior scale. Hierarchical linear modes were applied to analyze the data. When demographic and human capital variables (i.e., gender, age, marriage, educational level and organizational tenure) were controlled, hierarchical linear modeling results revealed that work team members’ supervisor career support was positively related to their psychological capital and organizational citizenship behavior. In addition, work team members’ psychological capital was a mediator between supervisor career support and organizational citizenship behavior at both group level and individual level. Therefore, supervisor career support and psychological capital were valuable interpersonal and mental resource to build efficient work team. This study extended existing researches that focused solely employees’ variables from individual level to group level, developing multilevel theory in organizational psychology research. This study also suggested several practical implications that supervisor career support and psychological capital were key elements for building efficient work teams, especially work team members’ psychological capital. Entrepreneurs should construct supportive leader-member relations to improve team members’ psychological capital and positive work attitudes and behaviors.