In complex organizations, where decisions are made on daily basis, one of the primary factors for effectiveness and competitiveness, is ability to make a decision. Whether is about more or less important decisions, long term or short term effect, to reach a decision can include people at different levels of hierarchy. In a process of reaching decisions we choose one type of action between more options. Most of the decisions are reached by using simple and intuitively methods and having a consideration for specific elements such as experience, knowledge and available information. In modern organizations, who are exposed to unstable conditions and frequent and fast economical changes, processes of making a decisions are often complicated and dynamic, so they demand strict approach which will be based on analytic methods and mathematical models. The main goal of this Final paper is to analyze in theory, the importance of program solutions which contribute in process of support in reaching of rational decisions in organizations, with an accent on Data Mining as one of the most successful method for knowledge discover. This Final consists five chapters. In Introduction chapter I will define the subject and the goal of paper, sources and methods of collecting information as well as the content and structure. Second chapter will analyze Data Mining in general. Starting with definition, I will analyze the beginning of concept, I will compare it with traditional statistical models, and infrastructure needed for to use it, will be processed. Third chapter will analyze phases of process, tehniques and methods which are used in process itself. Fourth chapter, the main one, will process in exact way, the areas where Data Mining concept is used and will analyze programs for using it. In the last chapter, I will introduce you with the conclusion of this Final paper.