Mikhail Petrovich Frinovsky (Russian: Михаи́л Петро́вич Фрино́вский; 7 February 1898 – 4 February 1940) was a Soviet secret police official who served as a deputy head of the NKVD under Nikolai Yezhov during the Great Purge.

Frinovsky was a revolutionary during the Russian Revolution and rose through the ranks of the Cheka and its successor agencies. Frinovsky was actively involved in the Great Purge and personally led the mass arrests and executions of security and military officials across the Soviet Union from 1937 to 1938. Frinovsky was made People's Commissar of the Navy of the Soviet Union in 1938 when he was himself removed from power and purged along with Yezhov. Frinovsky was arrested in 1939 on conspiracy charges and executed in 1940.

Mikhail Petrovich Frinovsky was born 7 February 1898 in the village of Narovchat in the Penza Governorate of the Russian Empire, into a Russian family. His father was a teacher and he studied in a religious Orthodox school in Krasnoslobodsk prior to World War I. In January 1916, Frinovsky volunteered for the Imperial Russian Army, serving as a sergeant in the cavalry until his desertion in August. He subsequently joined an anarchist group and began working as an accountant at a military hospital.

In March 1917, during the February Revolution, Frinovsky took part in the assassination of Major-General Mikhail Antonovich Bem, a distinguished army officer who was suppressing anti-war protests in Penza. He was also active during the July Days in Petrograd. In September, he volunteered for the Red Guard in Khamovniki district of Moscow. A month later, when the October Revolution occurred, the Red Guard unit under his command participated in storming of the Kremlin during the Moscow Bolshevik Uprising. Frinovsky was severely wounded and spent months recovering at a hospital in Lefortovo. Between March and July 1918, Frinovsky again returned to civilian life and worked as a deputy administrator of the Hodynskaya Clinic.

In July 1918, he joined the Russian Communist Party (b) and volunteered for the Red Army. Frinovsky was made a commissar of a combat unit and also head of the Special Section (the political supervisor and representative of the Cheka, the Bolshevik secret police) of the 1st Cavalry Army.

In 1919, Frinovsky was transferred to the Cheka full time, and became a deputy of the Special Section for Moscow later in the year. In this capacity, he participated in many operations most vital for survival of the Bolshevik regime, including actions against anarchists and rebel militias in Ukraine. From December 1919 until April 1920, Frinovsky served in the Special Section for the Southern Front of the Red Army. In 1920, he was transferred to the South-Western Front, where he served as chief of the Special Section, and as deputy to the Chief of the Special Section of the 1st Cavalry Army. In 1921, Frinovsky was appointed the deputy of the Cheka of Ukraine. From 1922 to 1923, Frinovsky headed the Kiev division of the GPU, the successor to the Cheka. From 23 June, he was also head of the OGPU (successor of the GPU) of the South-East.

In November 1923, Frinovsky was transferred to the Northern Caucasus and given command of the OGPU's Special Section for the North Caucasus Military District. He was made responsible for border security along the Black Sea coast in the region.

In July 1927, Frinovsky was transferred to Moscow, this time as aide to the commander of the Special Section for the Moscow Military District. In 1927, he completed high-command courses at the Frunze Military Academy. From 28 November 1928 until 1 September 1930, he served as the commissar of the Special Forces division assigned to the Dzherzhinsky College of the OGPU.