At the 1964 Olympic Games in Innsbruck, Mäntyranta added two more gold medals, winning the 30km race by 71.6 seconds and the 15km by 40.7 seconds. He also gained a silver medal in the relay.
In 1968, the skiier won a bronze medal at 30km and silver at 15km, missing gold in the latter race by less than two seconds. In the relay Eero skied the anchor leg for Finland. He managed to gain 26 seconds on Vyacheslav Vedenine of the USSR and passed him at the finish line to earn a final bronze medal.
Throughout his career, Mäntyranta was suspected of blood doping because his red blood count was 20% higher than that of other athletes. Thirty years later, scientists tested 200 members of his family and discovered that fifty of them, including the Olympian, were born with a rare genetic mutation that causes an increase in oxygen-rich red blood cells.