The founder of Modern Portfolio Theory was H. Markowitz, who in 1952 presented a model that allowed investors to choose the optimal portfolio in accordance with their own preferences. His model made it possible to optimize return and risk by introducing more securities into the portfolio. The concept of diversification is associated with this way of investing, and the rest depends on the investors, whether they are inclined to take more risks or not. This proves that it is more stable to invest in a portfolio consisting of several shares. The optimal portfolio is positioned on the efficient frontier, at the point that achieves the highest return with the appropriate risk rate. Through empirical testing, it is shown where the observed share of Atlanska plovidba is located on the efficient frontier, and whether it participates with its share in the optimal portfolio. Unfortunately, the results show that, like most of the selected stock of index, Atlanska plovidba achieved a negative return in 2022, with higher risk. Thus, one does not participate with any share in the optimal portfolio, on the contrary, it is positioned far from the Efficiency frontier. Therefore it is shown as not suitable for investment.