Mera was transferred to the private San Rafael hospital in Coruna, northern Spain, where she died Thursday evening, a hospital source said. She had been on holiday in Menorca with her daughter Sandra.
Listed by Forbes this year as the world's 195th richest billionaire with a fortune of USD 6.1 billion, the highest-placed among Spanish women, she was also described as the richest self-made woman in the world.
Inditex released a statement expressing the group's sadness over Mera's death.
"The group wishes to send its sincere condolences to her loved ones and friends at this extremely difficult time, after the loss of a person who contributed so much to the origins and development of the company," it said.
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Besides Zara, the Inditex group owns a number of successful international brands including Massimo Dutti and Pull and Bear.
She also held 30.6 per cent of hotel chain Room Mate, it said.