The siege of Mikhailovsky (Adyghe: Михайловски Къэуцухьэ; Russian: Оборона Михайловского укрепления) took place on 3 April 1840 during the Russo-Circassian War. The Circassians defeated the Russian defenses and won the siege. Unwilling to accept defeat, Russian soldier Arhip Osipov infiltrated the powder magazine and detonated the explosives, killing himself, the remnants of the garrison, and a significant number of Circassians. The action was praised in the history of the Russian Army and was described as "symbolic immortality".

The Russo-Circassian War had been going on since 1763. The Russians had been landing and building fortifications on the Black Sea coast of Circassia for a long time. The Russians began to strengthen their fortifications by making more landings on the Black Sea coast and gained control and gathered a large army. In 1834, Tuqhuzhuqo Kizbech, with 1,700 soldiers, trapped and destroyed a Russian army of 14,000. In the same year, he trapped and destroyed another Russian army of 6,000 with 1,200 soldiers. Then he destroyed many Russian garrisons, including Maryanskaya, Georgie, Afepskaya and Apenskaya. In 1837, he captured the Nikolayev fortification. After all these defeats, the Russians thought that there should be a stronger fortification in the region. The Mikhailovsky fortification began to be built in 1837 at the mouth of the Vulan River to establish control over the region. Its length was about 200 fathoms. The firing line was very wide and its length reached 540 fathoms. It was one of the strongest Russian fortifications in the region.

Circassians, led by Ismail Berzeg, tried to prevent construction by attacking in 1837. From 1839 the fortification was given to the command of the 1st division of the Black Sea coastline. The head of this division was Rear Admiral L. M. Serebryakov, and the head of the entire coastline was Lieutenant General N. N. Rayevsky. After Circassian victories in other sieges, the garrison was reinforced, Eight cannons were installed on the bastions.

The idea of establishing the Black Sea coastline belonged to Tsar Nicholas I. However, for various reasons, the fortifications were ineffective. Russian generals in the region considered the strategy of building fortifications to be completely unnecessary and that Alexey Yermolov's "strategy of terror" was more effective. However, Tsar Nicholas continued the construction of the fortifications.

Cast iron cannons of various calibers and ammunition were placed on the ramparts. The Circassians rarely used such technologies, so the Russians had a technological advantage.

The Circassians had cut off land communications between the coastal fortifications and the main Russian command. Therefore, in case of military danger, the Russian garrisons had to rely only on their own forces, without any hope of external help. Food was delivered to the fortifications by sea twice a year, and occasionally cruisers came along the way to pick up the sick.

The Treaty of Edirne was signed on September 14, 1829.  According to this treaty, the Ottoman Empire recognized the Caucasus, including Circassia, as Russian territory. The Circassians did not believe in the authenticity of this treaty. After the authenticity of the treaty was confirmed, Circassian ambassadors were sent to England, France and the Ottoman lands to inform them that the treaty was invalid for the Circassians. Russia used this treaty to strengthen its claim that Circassia belonged to it.

The Circassians were secretly supported by Turkish and British adventurers. In the traditional people's assembly, the Circassians decided to end all relations with the Russians and continue to resist Russian expansion.