Abstract: Landlocked parcels are frequently produced by subdividing larger parcels of land before the land planning and Building Act were established to limit the building development and construction with public road frontage. Due to lack of public access, public services, police and fire protection, landlocked parcels are neglected in real estate investment and urban development, causing deterioration and isolation of center parcels without road frontage in urban blocks and increasing the exposure to the risk of crime and slumism. Although an easement agreement is sometimes permitted for a new construction, validity of the easement pending upon the land ownership changes make the development of landlocked parcels unstable and unsustainable. However, building on landlocked parcels permitted before establishment of Building Act can be remodeled to accommodate new programs and improve the environment quality as long as building occupancy classifications don't need to be changed. Landlocked parcels can be discovered in dense residential districts without large-scale development, which might be underdeveloped and lagging in community and cultural services. Sometimes landlocked parcels also are found in over-developed districts, making the block privatized and gated. In this paper, typologies of landlocked parcels with existing building in Seoul are described to categorize landlocked parcels, its urban block and district as well as to examine its urban conditions and problems. This categorization allows evaluating the effectiveness of regeneration. Also programs possible to landlocked parcels are explored depending on various lot sizes, frontage conditions, and construction types of existing buildings, from the viewpoint of public investment to lead the development of landlocked parcels for more public and community values. Public investment on remodeling of a building on landlocked parcels in Seoul would contribute to regenerating the parcel, the block and the community, enhancing the value of parcel and driving the sustainable urban transformation.