The US Food and Drug Administration (FDA) will allow gay men to donate blood if they have been celibate for one year - lifting a 30-year ban.
Some gay activists called the one-year rule discriminatory, but it matches policies in other counties including the UK, Australia and Japan.
The ban was put in place at the start of the Aids crisis during the 1980s.
Groups that handle blood donations lobbied for the change, calling the ban on gay donors "medically unwarranted".
While calling the decision a "step in the right direction", activist David Stacy said the FDA needs to go further.