This study investigated the mediating effect of job satisfaction on the relationships between internal communications, professional development, empowerment and prosocial service behaviors. There was almost no research exploring job satisfaction's mediating effect on first line civil servants' work attitude in Taiwan. This paper collected 346 valid samples from first line civil servants in Taiwan and used structural equation model to test the hypothesis established. The results confirmed that: internal communications, professional development, empowerment positively influenced job satisfaction. Job satisfaction positively influenced prosocial service behaviors. Job satisfaction partially mediated the relationships between internal communications, professional development, empowerment and prosocial service behaviors.