Mary Lines (later Smith, 3 December 1893 – December 1978) was a British athlete. She competed in the long jump and 60 m – 800 m running events at the 1921 Women's Olympiad, 1922 Women's Olympiad and the 1922 Women's World Games and won nine gold, two silver and one bronze medals. In 1924 she participated at the 1924 Women's Olympiad and won the gold medal in the 100 yards running and the long jump. In 1922 she participated at the Women's Olympiad in Paris and won the gold medal in the 4×110 yds relay (with Lines as first runner, , and Gwendoline Porter) setting a new world record. In 1923 she participated in the first WAAA Championships becoming british champion both in running 100 yards, 440 yards and hurdling as well as in the long jump.