The paper analyses the legal construction of the shares of Polish public companies in the 18th century. The analysis relied on the statutes and documents referring to the shares. The Woolen Products Manufacturing Company founded in 1766 should be considered the first Polish public company. Before 1795, i.e. after Poland lost her independence due to the third partition of the country, there had been established as many as seven companies of that type. The surviving projects of statutes show that the founding of several other companies was planned. The period in which the first Polish companies functioned was short and most of them were dissolved within a few years after they had been founded. This was due inter alia to the difficulties in collecting the capital fund. The preserved source materials allow for the analysis of the legal nature and function performed by the shares in the construction of these companies. The author believes that – in the light of statutory provisions and the documents referring to the shares - it is possible to regard the shares connected with the companies as a part of joint stock capital and the entirety of the rights of the shareholders and also disposable securities. In particular, the shares of the first Polish public companies may be attributed the nature of the part of joint stock capital of the value determined in the statute. This capital, collected through contributions made by the partners in return for obtaining a specified number of shares, was the basis on which there functioned each of the companies subjected to the analysis.