The first time for female athletes to participate in the modern Olympic Games was the second Olympic Games in 1900. Only free male Greek citizens were allowed to participate in the 1st modern Olympic Games as well as the ancient Olympic Games.
According to the IOC (International Olympic Committee), only 12 female athletes participated in the second Olympic Games out of the 1066 athletes from 19 countries. They competed in only two events which were golf and tennis. In the 3rd St. Louis Olympics, archery was the only women's event. In the 4th London Olympics, archery, figure skating, and tennis became women's events, and diving, swimming and tennis in the 5th Stockholm Olympics.
Read about more key dates for women in the history of the Olympic movement here.