Leantsiuk came third at the Belarusian championships in 2003 and won the national junior title with a new best throw of . She was runner-up to Russian rival Anna Avdeyeva at the 2003 European Athletics Junior Championships. She did not improve in 2004 – her first year of full senior competition – but managed a throw of at the 2005 European Athletics U23 Championships, taking fourth place. She cleared eighteen metres for the first time in 2006 and ended the year with an improved personal best of . She was also second in the First League meeting of the 2006 European Cup.