Sergey Sergeyevich Kamenev was a Soviet military leader who reached Komandarm 1st rank.

Sergey Petrovich Kapitsa was a Russian physicist and demographer. He was best known as host of the popular and long-running Russian scientific TV show, Evident, but Incredible. His father was the Nobel laureate Soviet-era physicist Pyotr Kapitsa, and his brother was the geographer and Antarctic explorer Andrey Kapitsa.

Sergey Georgyevich Kara-Murza is a Soviet and Russian chemist, historian, political philosopher and sociologist.

Sergey Alexandrovich Karjakin is a Russian chess grandmaster. A chess prodigy, he previously held the record for the world's youngest ever grandmaster, having qualified for the title at the age of 12 years and 7 months.

Sergey Pavlovich Karpov is a leading Russian Byzantinist who specializes in the Empire of Trebizond and the history of Gazaria. His work in Italian archives helped bring to light the records of Genoese and Venetian notaries and accountants concerning their Black Sea colonies. Some of his monographs are available in Italian translation. He was awarded a State Prize in 1996 and was elected into the Russian Academy of Sciences in 2003. Karpov was Dean of the Department of History of the Moscow State University from 1995 until 2015.

Sergey Khoruzhiy was a Russian physicist, mathematician, philosopher, and theologian.

Sergey Antonovich Klychkov was a Russian poet, novelist and translator.

Sergey Kolesnikov is a Russian judoka. He competed in the men's lightweight event at the 1996 Summer Olympics.

Sergey Nikolayevich Kolosov was a Soviet and Russian film director, screenwriter, and pedagogue. People's Artist of the USSR (1988).

Sergey Mikhailovich Koltakov was a Soviet and Russian actor.