Liquidity of company’s securities is of particular importance for investors who have invested their money in the company’s shares. If the shares have high liquidity, the owners can quickly sell them when necessary and they have nothing to lose but gain at best. However, if the shares can not be sold immediately, their price is considerably discounted when offering them for sale. The article is devoted to the problem of a correct definition of discount for illiquidity when assessing the cost of capital of a closed company and the role of adjustment for shares illiquidity when assessing value of assets.