Specialist graduate thesis deals with an analysis of the cost-effectiveness of investment in expanding activities such as company Inproteh. Inproteh, a manufacturer of fire-resistant and security doors, uses external services in own production, which causes high costs. Because of the cost problem, the work is based on the analysis of the viability of introducing the machines that are currently being used through external services. The research process has used the methods of environmental analysis – a PESTEL analysis, which defines factors with a negative and positive effect on the business of enterprise. A competitive analysis has revealed that there are several companies in the Republic of Croatia offering products similar to the company Inproteh. Taking into consideration the internal factors, a SWOT analysis confirms that the company possesses sufficient knowledge and experience in the production of security doors which is of great importance for competition in the marketplace. A financial plan defines a realization of the investment in the value of HRK 1.010.107,50. Due to the methods of assessing the financial effectiveness of the investment project, positive results has been appeared, which has indicated the cost-effectiveness of investment in a project. After assessing the financial efficiency of an investment project, the conclusion is composed by comparing the results. Company's access to the investment project would bring annual savings of HRK 127,161.