Abstract: Freedom is an important clue through Marx’s thoughts. Free labour is the fundamental way to realise freedom, which is a sign of human emancipation and individual liberty. Marx’s thoughts about free labour need to go back to the concept of “self-activity”. The concept of “self-activity” is not only a transcendence of Hegel’s “self-consciousness”, but also a renunciation of Hess’s “free action”, which denies purely mental activities and value suspensions. In Marx’s period of practical materialism, “self-activity” appeared as a critique of alienated labour, an affirmative aspect of the class nature of human. After Marx established his materialistic view of history, the concept of “self-activity” began to be associated with the contradictory movement of the productive forces and production relations. The concept of “self-activity” served as a precursor to Marx’s formal entry into the critical study of free labour in political economy.