Kateryna Lahno (born December 27, 1989) is a Ukrainian chess player and two-times European Champion.

She earned the FIDE title of Woman Grandmaster (WGM) at the age of 12 years and 4 months, breaking Judit Polgár's record to become the youngest ever to earn this title. She is now a full Grandmaster (GM). Born in Lviv, Lahno grew up in the industrial and chess-friendly town Kramatorsk. Since 2009 she lives in France with her husband GM and TV reporter Robert Fontaine.

Lahno was the fifth seed for the 64-player knockout 2004 Women's World Chess Championship. At the age of 15 she won the 2005 European Individual Women's Championship, held in June in Chişinău, Moldova. Tied with Russian IM Nadezhda Kosintseva at the end of the 12th round with 9 points each,

Lahno won both games of a two-game rapid-play tie-break playoff to win the championship. She won IV Women's 'North Urals Cup - 2006', attaining a full grandmaster norm in the process.

The same year, she became Russian Team champion with the club of Spartak, and then won the European Team championship in Ohrid. In August 2010, Kateryna won World Woman Blitz Championship.