This study investigated the mediating effect of civil servant’s positive affect on the relationships between autonomy, competence, relatedness need and autonomous motivation. There was almost no research exploring the mediating effect of positive affect on civil servants’ work attitude in Taiwan. This paper collected 256 valid samples from civil servants in Taiwan and used structural equation model to test the hypothesis established. The results confirmed that: autonomy, competence, relatedness need positively influenced positive affect. Positive affect positively influenced autonomous motivation. Positive affect partially mediated the relationships between autonomy, competence, relatedness need and autonomous motivation.