Previous studies have not sufficiently investigated how supervisors can improve employees’ intention to help their colleagues. Therefore, research regarding this issue is required. Social exchange theory and the appraisal-coping model were adopted herein to hypothesize that supervisor-employee guanxi—informal interpersonal connections that involve the exchange of favors—and a supervisor’s negative mood are associated with employees’ intention to help their colleagues. The findings indicate that employees’ intention to help their colleagues is negatively related to their supervisor’s negative mood but positively related to employee agreeableness. Furthermore, for employees who have weak guanxi with their supervisors, the negative mood of the supervisors is negatively related to the employees’ intention to help colleagues, but this relationship does not apply to employees who have strong guanxi with their supervisors. The findings suggest that supervisors should manage their negative moods and strengthen their guanxi with employees to improve their employees’ intention to help colleagues.