Enterprise social media (ESM) has been considered as an emerging platform for employees to deal with uncertainties in external environment to attain agility performance. However, the underlying mechanism through which using ESM enhances agility performance remains unclear. The current study is an effort to explore the mediating effect of psychological conditions based on self-determination theory. Specifically, this research proposes a model to examine how the effect of ESM usage is translated into workforce agility (i.e., proactivity, adaptability, and resilience) through psychological conditions (i.e., psychological meaningfulness, psychological availability, and psychological safety). By collecting data from 167 employees who adopted ESM in workplace, most mediating effects are supported. This study not only enriches ESM research by providing a psychological insight to interpret its influencing mechanism, but also offers practical suggestions for managers to take care of psychological conditions of employees to realize the value of ESM.