This article analyzes the attitude of Russian diplomacy regarding the events in the Romanian Principalities/Romania in 1866, the plans for a European congress in late July, and the discussions in August-September about the denunciation of the article concerning the neutralization of the Black Sea in the Treaty of Paris (1856). It is noticed that, following the abdication of the Prince Alexandru Ioan Cuza in February 1866, the Russian Foreign Minister A.M. Gorchakov had consistently opposed the arrival of a foreign prince, believing that previous treaties regarding the status of the Principalities should be respected. At the same time, Russian diplomacy supported the disunity of the Principalities and the separatist movement in Iași on April 3/15, 1866. The events in the Romanian Principalities would take a back seat in the context of the outbreak of the Austro-Prussian War in mid-June 1866. Under these conditions, Russian diplomacy tried in the summer of 1866 to summon a European congress, but the European cabinets refused. In August-September, Gorchakov prepared several internal documents that provided for the removal of the “stigmas” of 1856, but Tsar Alexander II did not agree that the proposal to revise the article on the neutralization of the Black Sea in the Treaty of Paris should be sent to the Great Powers.