The aim of the PTSL program is to accelerate land registration in Indonesia to provide legal certainty for community land rights. However, PTSL's activities did not all run smoothly. Therefore, the emergence of these Cluster 3 land parcels can hamper the activities of accelerating land registration. The existence of rejection by traditional institutions is one form that can hinder the course of PTSL activities. The purpose of this research is to find out the process of several land parcels in Mambi Kelurahan categorized in Cluster 3 in PTSL activities and to seek settlement of cluster 3 land parcels in Mambi Kelurahan to be certified. This research was conducted using qualitative methods with a descriptive approach. Mambi sub-district was the chosen research area because it has a high number of cluster 3 fields. Qualitative data collection was carried out using interviews, observation, and document studies.
From the results of the research it is known that the problems with the certificate of cluster 3 land parcels in PTSL activities in the Mambi Village were due to the rejection by the Customary Institution. Where customary institutions claim that the land is customary land. As for efforts to resolve the problem of cluster 3 land parcels, namely conducting a review of Regional Regulation Number 10 of 2021 concerning Indigenous Peoples where to identify an area in which there are indigenous peoples must have 4 criteria, namely having the history of the area, having a clear territory, having customary institutions and have customary law.

Keywords: PTSL, Cluster 3, Rejection of Traditional Institutions