His first novel, Lalande 21185, appeared in 1966, a year after his first short-story anthology, and was geared toward young adults. By 1982 he had published four more collections: Przejście przez lustro (Through the Mirror, 1975) Iluzyt (1976) Feniks (The Phoenix, 1981) and Ogon diabła (The Devil's Tail, 1982). His first book was published in 1965, a short-story anthology, Jad mantezji ( The Venom of Mantesia), which included stories from Młody Technik and some others that had already appeared a year earlier in another anthology. Other stories by him soon appeared in several other Polish magazines.

In 1961 Młody Technik published Zajdel's science-fiction debut, the short story ' Tau Ceti' ( Polish: Tau Wieloryba). With his brother, he started a column in a Polish magazine for young people interested in science and engineering, Młody Technik ( Young Technician), in which they proposed various futuristic gadgets. In his spare time, he popularized science by writing science fiction. He published a number of academic works, handbooks of safety regulations, as well as educational and popular science texts. After graduating, he worked many years as a radiological engineer and an expert on nuclear physics at the Central Laboratory of Radiological Protection in Poland. He studied physics at the University of Warsaw. Janusz Zajdel was born 15 August 1938 in Warsaw, Poland. The Polish science fiction fandom award was named after him: the Janusz A. His heroes desperately try to find meaning in the world around them. His main recurring theme involved the gloomy prospects for a space environment into which mankind carried totalitarian ideas and habits: Red Space Republics, or Space Labor Camps, or both. His major genres were social science fiction and dystopia. Janusz Andrzej Zajdel (15 August 1938 – 19 July 1985) was a Polish science fiction author, second in popularity in Poland to Stanisław Lem.

Limes inferior by Janusz A. Zajdel