Sergei, in the works of Harry Turtledove, may refer to:

Sergei (Black Tulip), fictional Red Army soldier, POV of "Black Tulip".
Sergey Gorshkov, historical Soviet admiral referenced in Aftershocks.
Sergei Izvekov, a Russian colonist on Haven in "Hang Together".
Sergei Morozhin, minor fictional character in Worldwar.
Sergei Pavlov, fictional Russian ambassador, minor character in The Two Georges.
Sergei Tolmasov, fictional cosmonaut and POV in A World of Difference.
Sergei Yaroslavsky, fictional Red Air Force pilot and POV in The War That Came Early.
Sergei Yaroslavsky's Mother is referenced in West and East.