Pseudo-Geber ("false Geber") is the name assigned by modern scholars to an anonymous alchemist born in the 14th century, probably in Spain. He wrote a few books on alchemy and metallurgy, in Latin, under the pen name of Jabir Ibn Haiyan (usually rendered Geber in Europe) — after the foremost 8th century Islamic alchemist with the same name.

Books by the real Jabir Ibn Hayyan had been translated into Latin during the 11th to 13th centuries, and had made a profound impression on European alchemists. Pseudo-Geber probably adopted the name of his illustrious predecessor in order to capitalize on his reputation. In any case, Pseudo-Geber's work reflects 14th century European alchemical practices rather than earlier Arab ones.

Four of his works have suvived, dated from about 1310:

• Summa perfectionis magisterii ("The Sum of Perfection or the Perfect Magistery")
• Liber fornacum ("Book of Furnaces"),
• De investigatione perfectionis ("On the Investigation of Perfection"), and
• De inventione veritatis ("On the Invention of Verity").

Being the clearest expression of alchemical theory and laboratory directions available until then — in a field where mysticism, secrecy, and obscurity were the usual rule — Pseudo-Geber's books were widely read and extremely influential among European alchemists.

Pseudo-Geber was instrumental in spreading Islamic alchemical theories throughout western Europe. He assumed that all metals are composed of sulfur and mercury and gave detailed descriptions of metallic properties in those terms. He also explained the use of an elixir in transmuting base metals into gold (see philosopher's stone).

Pseudo-Geber's rational approach, however, did much to give alchemy a firm and respectable position in Europe. His practical directions for laboratory procedures were so clear that it is obvious he was familiar with many chemical operations.

Pseudo-Geber's works on chemistry were not equaled in their field until the 16th century with the appearance of the writings of the Italian chemist Vannoccio Biringuccio, the German mineralogist Georgius Agricola, and the German alchemist Lazarus Ercker .