This article aims to establish Mill's theory of liberty as a theoretical model of 'social liberalism' and examine its characteristics, paying attention to the relationship between liberty and society. To this end, we first examine the meaning horizon of social liberty that Mill spoke of in his On Liberty(2). For him, social liberty is both passive and active, and aims for a free individual and a free society at the same time. A society in which individual freedom is maximized is a free society. Mill notes that society suppresses individual liberty when dominated by the popular opinion of the majority. I critically examine Mill's view of public opinion and democratic publicity that suppresses freedom(3). In this chapter, I evaluate Mill's social liberty as having two semantic horizons: limiting power and realizing individuality. However, he is suspected of denigrating society as a battleground of corrupted desires by taking the view that the power to be restricted for freedom is the socially formed opinion and will. Because Mill paid too much attention to the possible harms of 'tyranny of the majority', his liberalism runs the risk of being distorted into antisocial individualism or the elitism of creative individuals. In order to examine the scope of the validity of this criticism, it is necessary to examine the characteristics of deliberative democracy in his Considerations on Representative Government(4). His theory of democracy, which focused on participation, cooperation, discussion, and deliberation, seems to provide a basis for reconstructing his theory of liberty as a model of social liberalism. His model of liberalism based on the reciprocity of freedom and society appears to be liberal socialism(5).