Lambda Kappa Sigma (ΛΚΣ or LKS) is an international pharmacy fraternity headquartered in Muskego, Wisconsin.

LKS is the oldest and largest professional pharmacy fraternity for women in the world.

On October 14, 1913, Ethel J. Heath and eight other female students at the Massachusetts College of Pharmacy organized Lambda Kappa Society, a social club.

At that convention, the delegates voted to join the Professional Panhellenic Association, becoming the first pharmaceutical sorority in the PPA.

During the 1988 biennial convention, the members voted to delete all gender references from the fraternity's membership requirements.