Tin is one of the vital raw materials in the manufacture of mobile phone components. The components produced by the domestic mobile phone industry are important to increase the Local Content Requirements (TKDN) in each product produced by the industry. Therefore, the downstreaming of tin becomes an important thing and can encourage the fulfillment of TKDN in mobile phone. However, the problems faced by the domestic mobile phone industry are the regulations applied to the mobile phone industry, the lack of quality of local labor to master the technology used, and the lack of interest of foreign investors to invest in the mobile phone industry sector related to illegal mining and investment policies. This research aimed to identify problems in the implementation of the law and import substitution implemented by the government that resulted in many mobile phones that are below TKDN, so that in writing this research it will be based on the theory of legal certainty and theory of import substitution. The theory of legal certainty is used to see whether the legislation on tin, investment, mobile phone and the industry is running well or not. Theory of substitution import is used to see how import substitution works and its application since import substitution was implemented in Indonesia. To research, the author will use normative research using secondary data, and by analyzing the data qualitatively. Based on the research results, The regulations that apply to mobile phone and industries still find problems where there are no administrative sanctions applied if there is a violation. then the downstreaming of tin has not been pursued as much as possible by the government so that it cannot be made into value-added tin that can be used as a mobile phone component. The interest of foreign investors to invest in mobile phones in Indonesia is also still low due to the large number of illegal tin mining, and the difficulty of licensing to invest in the tin and mobile phone industry.