Perpignan - France's women's world featherweight champion Angelique Duchemin died aged 26 on Tuesday after suffering a heart problem in training.
Duchemin fell ill at her boxing club in Thuir in the Pyrenees Orientales region on Monday evening.
She received a cardiac massage before being rushed to hospital in Perpignan, the head of the local boxing federation Jacques Rovira told AFP.
She passed away in hospital on Tuesday morning, apparently of a pulmonary embolism, Rovira added.
Duchemin, whose father, also a boxer, died of a heart attack in 2013, was a double champion of France and Europe in 2015 and won her world title in May.
She was due to defend her title on October 12 in Montpellier.
France's Olympic champion, Estelle Mossely, posted on Twitter: "It's with sadness that I heard about the death of Angelique Duchemin! We started out in the team together. So young... my condolences to her family."