Most of the local communities living around the forest fulfil their daily needs, depending on the forest resources, but the government and even global policy have enacted the forest as a protected area or national park. The purpose of this research is to understand and explain the principles of customary law concerning the natural resources that exist in the national park, and to determine the effectiveness of customary law in protecting these natural resources. The research method applied to explore community values and attitudes is socio-legal. The research revealed society's habits through exploration, and norms and the rule of law are embraced. Some principles of customary law on natural resources include palia (taboo) and ombo (prohibition) pertinent to natural resource conservation. Both of these principles are adhered to and have been hereditary. The values on utilising natural resources are still complied with (effective), although state law takes a formal approach for any infringement surrounding the national park. However, customary law principles still always need to be a source for environmental or related law.