ENThe analysis of the centralization of the state in historiography in the period of the Four-Year Sejm (in 1788-1792) up to now has been mostly limited to the discussion of the resolutions passed by the Sejm, not looking more deeply into the practical aspect of the connection of public administration institutions, without analyzing how, in what manner this merger was implemented, and what problems of an administrative nature it created. The aim of this article - relying on the example of the reorganization of the Treasury Commission to discuss the problem of the "merger" of Lithuanian state institutions with the Polish institutions from the adoption of the 3 May 1791 Constitution to the abolition of the activities of the Treasury Commission of Both Nations on 18 August 1792. Particular attention in the article is given to the law of 10 October 1791 on "The Reciprocal Guarantee of the Two Nations" (Polish "Zaręczenie wzajemne Obojga Narodów"), and the "Act of the Treasury Commission of the Both Nations", adopted on 27 October 1791. The analysis of the decisions of the Sejm, the documents of the Law Guard and the sources of Lithuania's Treasury Commission in 1791-1792 one comes to the conclusion that the establishment of the Laws Guard did not introduce any major changes in the structure of the Treasury administration because the Treasury Ministers section of this institution essentially took over the functions of the eliminated authority of the Permanent Council of the Treasury Department.Both after the declaration of the 3 May 1791 Constitution and the establishment of the Law Guard, after adopting the law of the Mutual Guarantee of Both Nations as well as the law of the Treasury Commission of Both Nations, the old treasury system actually still functioned. The transition period of the reform of the treasury administration was from 3 May 1791 up to 1 February 1792. During this period the Lithuanian Treasury Commission essentially remained a separate institution, concerned with the affairs of the Grand Duchy of Lithuania. The Crown Treasury Board took care of the affairs of the Polish Treasury. Various types of problems, related to the organization of the Chancellery's work, the payment for the work of officials, the protection of the archives and the administration of justice, accompanied its activities. The largest changes occurred in the area of the court treasury. In the period from 1 February 1792 essentially the cases assigned to the Treasury court were not decided, because the law of Lithuania's Treasury Court was not adopted and this institution in general had not been established. The Treasury Commission of Both Nations actually existed from 1 February to 18 August 1791, when by the instruction of the Targowica Confederation the Law Guard and the ministries subordinate to it were abolished and the order of the management of the treasury valid until 1788 was restored. The period of the existence of the Treasury Commission of Both Nations was too brief to have had the possibility to essentially impact the financial administration of the state and to create a model of the centralized management of the state.