Oleksandr Serhiiovich Pyatnytsya (Ukrainian: Олександр Сергійович П'ятниця; born 14 July 1985 in Dnipropetrovsk) is a male javelin thrower from Ukraine.

His personal best is 86.12 metres, achieved in May 2012 in Kyiv, which was a new national record.

He won the bronze medal at the 2007 European U23 Championships and finished fifth at the 2009 World Athletics Final.

In 2016 a reanalysis of samples from the 2012 Olympics resulted in a positive test for the anabolic steroid turinabol.

He was stripped of his title by the IOC and ordered to return his silver medal, medalist pin and diploma.