Alfred Marshall Mayer (born in Baltimore, Maryland, 13 November 1836; died in Maplewood, New Jersey, 13 July 1897) was an American physicist.

In 1856 he was called to the chair of physics and chemistry in the University of Maryland, and from 1859 to 1861 he held a similar post in Westminster College, Missouri.

At Lehigh, he had charge of the department of astronomy, and superintended the erection of an observatory, from which he made a series of observations of Jupiter.

In 1873 he was one of the associate editors of the American Journal of Science, but after a year's service withdrew on account of failing eyesight and went to visit England.

He contributed to the Scientific American Supplement during 1876-1878 an extensive series of papers “On the Minute Measurements of Modern Science.” His other memoirs include: Besides his numerous articles in his special branches of inquiry contributed to cyclopædias and journals, he published: His brother Francis Blackwell Mayer was a noted painter.