Social media (SM) allow citizens to not only read news but also express their political opinions. Drawing from cognitive appraisal and affective intelligence theory, this study investigated the affective foundation of political opinion expression on social media (POESM) using two-wave panel data. The results indicate that enthusiasm and anger stimulated POESM but only for individuals with a minimum threshold motivation to use SM for political purposes. Among the politically motivated, anxiety increased POESM for individuals with low political knowledge but lessened POESM for ones with high political knowledge. Thus, emotional states can be powerful drivers of POESM. In contexts with low levels of POESM, emotions may stimulate online discussion as well as contribute to the further emotionalization of political debates.