Sugimori abruptly resigned in August citing personal reasons, despite the oil and metals company posting strong first-quarter results.
On Wednesday, state broadcaster NHK quoted Eneos as saying Sugimori sexually harassed a woman in July.
Without claiming that the harassment was sexual in nature, Eneos, Japan’s largest oil refiner, said in its statement that it had investigated the allegations made against Sugimori and concluded that he had “engaged in inappropriate” and asked him to resign.