The issues of proprietorship have been controversial throughout the human history. On the basis of the fabulous works of Rousseau on proprietorship,this paper attempts to discuss the legitimate basis of proprietorship,as well as its necessity for human society which explains the converting process from possession to proprietorship. Rousseau believed that personal desire and labor were factors consisting of the fact that human beings possessed materials.If pursuing the reason for ownership,other factors should be considered. Only when the state w as founded and possession w as protected did possession change into the so-called private property. In other words,Rousseau believed that the real basis of ownership was the social acknow ledgement. At the same time,through analyzing and comparing relative theories of nomologists and philosophers,the thoughts of R ousseau on ownership are highlighted. The issues of proprietorship have been controversial throughout the human history. On the basis of the fabulous works of Rousseau on proprietorship, this paper attempts to discuss the legitimate basis of proprietorship, as well as its necessity for human society which explains the converting process from possession to proprietorship. Rousseau believed that personal desire and labor were factors consisting of the fact that human beings possessed materials. If pursuing the reason for ownership, other factors should be considered. Only when the state w as founded and possession w as protected did possession change into the so-called private property. In other words, Rousseau believed that the real basis of ownership was the social acknow ledgement. At the same time, through analyzing and comparing relative theories of nomologists and philosophers, the thoughts of Rousseau on ownership are. highlighted.