Sergey Kasnauskas (Belarusian: Сяргей Каснаускас; born 20 April 1961) is a Belarusian former track and field athlete who competed in the shot put for the Soviet Union. As of 2016, he places within the world top 25 all-time for the event. He was a bronze medallist at the 1979 European Athletics Junior Championships behind future world medallist Remigius Machura. His outdoor mark stood as the Belarusian national record until 2011, when it was beaten by one centimetre by Andrey Mikhnevich.