Gee whiz! I just looked up Antimatter in Wikipedia (or do we say "on Wikipedia?" "At Wikipedia?"), and under "Antimatter in fiction" a lot of trivial information was deleted. It was replaced with a succinct summary of my recent
Symmetry article.
There is a long history of the appearance of antimatter in the Science Fiction genré. The very first use was a short story which appeared in the July 1942 issue of the magazine Astounding Science Fiction. The story had been commissioned by the magazine editor John W. Campbell, Jr. after he heard of scientific controversies over whether asteroid sized pieces of "contraterrene" (antimatter) might actually exist. Campbell first offered the commission to Robert Heinlein but after he refused the story went to Jack Williamson. Williamson's short story Collision Orbit appeared under his pseudonym Will Stewart.
Thanks to encyclopedist "SpinningSpark" for the vote of confidence. I am impressed with SpinningSpark's speed; the article appeared online only on 30 September, and the Antimatter revision occurred on 4 October.
(I do understand that this bit of glory can vanish as quickly as it was bestowed.)
Actually, "Collision Orbit" was not the first use of antimatter in an SF story. I took pains to avoid claiming this in the article, but the title "Antimatter's Science Fiction Debut" wound up being used. Sorry.
The earliest SF story I have found about antimatter is John D. Clark's "Minus Planet," in the April 1937 Astounding. It's anthologized in Asimov's
Before the Golden Age.