Sergiy Demchuk (Ukrainian: Сергій Демчук) is a paralympic swimmer from Ukraine competing mainly in category S12 events.

In 2004 he was part of the Ukrainian squad that broke the world record and won gold in both the 4 × 100 m freestyle and the 4 × 100 m medley.

He was not as successful in individual events, he failed to make the final of the 50m and 100m freestyle and finished seventh in the 100m butterfly.

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