[2]: 87–88 His first published science fiction story was Bis zum Nullpunkt des Seins ("To the Zero Point of Existence", 1871), depicting life in 2371, but he earned his reputation with his 1897 novel Auf zwei Planeten, which describes an encounter between humans and a Martian civilization that is older and more advanced.

The book has the Martian race running out of water, eating synthetic foods, travelling by rolling roads, and utilising space stations.

His spaceships use anti-gravity, but travel realistic orbital trajectories, and use occasional mid-course corrections in travelling between Mars and the Earth; the book depicted the technically correct transit between the orbits of two planets, something poorly understood by other early science fiction writers.

[3] His last book was Sternentau: Die Pflanze vom Neptunsmond ("Star Dew: the Plant of Neptune's Moon", 1909).

For his writing (totalling around 420 works including non-fiction), Lasswitz has been called "the first utopistic-scientific writer in Germany" or even "a German Jules Verne".