Science Fantasy was a British science fiction and fantasy magazine of the 1950s and 1960s.

Originally launched in 1950 as a digest-sized companion to the science fiction magazine New Worlds, its first three issues were edited by Walter Gillings. John Carnell took over from 1951 until 1964 when both titles were sold, the format was changed to paperback size as an economy measure, and Kyril Bonfiglioli took over as editor. The magazine published a total of 81 numbered issues under its original name until its February 1966 issue.

It was then renamed Impulse and the numeration began again at 1. The change of title and numeration confused retailers and was bad for sales. Initially edited by Bonfiglioli, then by Harry Harrison and finally Keith Roberts, Impulse ran for 12 monthly issues before it was finally cancelled in 1967.

As its original name suggested, the magazine published a mixture of science fiction and fantasy stories (see science fantasy), with fantasy predominating under Carnell's editorship. Notable authors who contributed over the years included:

• John Brunner
• Kenneth Bulmer
• John Rackham
• Michael Moorcock (Elric stories)
• Thomas Burnett Swann ("Where is the Bird of Fire?" and other notable early works)
• Keith Roberts (Stories later incorporated into the novel Pavane; Roberts also contributed cover artwork 1964 - 1967 as well as editing the last few issues of Impulse)
• Chris Boyce

Science Fantasy is also notable for having published the first story by Terry Pratchett.

Some of the information in this article is derived from The Encyclopedia of Fantasy (1997), ed. John Clute and John Grant .