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Can a shareholder be liable in case of bankruptcy of one of the companies he invested in?
No, assuming by "public company" you mean a corporation.  The shareholder's individual liability is limited to their investment.  Your shares can go to zero value, but that's the limit. EDIT In regard to the follow-up question in the comments: "Are all companies in the stock market corporations?" the answer is definitely "no."  I cannot say much about other countries, but the US markets have some entities which are known as "master limited partnerships."  These trade shares on the market by the usual rules, but if you buy you become a partner in the company rather than a shareholder.  You still have limited liability in this case, but there will be differences, for example, in how you're are taxed.