This study examines the economic effects of ill-defined property rights on the resource usage with special reference to the Korean Green Belt. Property rights are considered ill-defined, when their whereabouts are not clearly delineated, they are not assigned to those who utilize them most efficiently, and they are not exercised precisely. If properly, and they are not exercised precisely. If properly rights are ill-defined, it is more likely that economic agents pursue opportunistic and illegal behaviors and even their rational behaviors tend to bring about undesirable outcomes, and social conflicts occur around the assignment of the rights. Upon the completion of a case study, we found that the ill-defined property right system of the Korean Green Belt has, in fact, resulted in several problems in resource usatge. Inefficient land use, compromising reassignment of property rights, the prevalence of illegal activities, huge management costs, and the spread of social conflicts are the problems in question. These problems can be resolved by the realignment of property rights, since they are caused by the ill-defined property right system. To resolve such problems, we need to reassign properly rights so that their delineation may be complete and those who value them highest may exercise the rights, and social justice in terms of wealth distribution may be achieved.