The Stock Exchange are organized places around the world where are traded with all securities. Relationship between supply and demand in the capital market depends on the growth and fall of the price of securities. There is a growing number of securities in the capital market and they differ in their value and degree of risk. This is why stock indexes are general indicators of the market and they are expressed numerically. With stock indexes it is possible to monitor the trend of certain groups of shares. Any change in the price of securities, in this case shares, also are changing stock index. CROBEX is the stock index of the Zagreb Stock Exchange, his constituents includes 25 of the highest ranking shares, respectively presents shares of representative companies. In addition, he is the main index of the Croatian capital market. Regular and extraordinary revision of Crobex decides which shares are going out and which are going to be included in the new constituents of the index. The movement of the CROBEX index due to the observed period will show movement of his value in index points. His reliability derives from the fact whether the prices of securities (shares) will tend to grow or fall.