Which C.S. Lewis novel is set partly on the planet Venus?

The C.S. Lewis novel set partly on the planet Venus is Perelandra.

Published in 1943, Perelandra is the second book in Lewis's Space Trilogy, also called the Ransom Trilogy. The story follows the philologist Elwin Ransom after he travels to the planet Perelandra, Lewis's fictional version of Venus. There he encounters a newly created world facing a temptation analogous to the biblical Fall.

The novel follows Out of the Silent Planet, published in 1938, and precedes That Hideous Strength, published in 1945. Although the trilogy uses interplanetary travel and speculative technology, Lewis combines those elements with theology, mythology, and philosophical questions about good and evil.

A common mix-up is treating Perelandra as the name of the trilogy or as a nonfiction account of Venus. It is specifically the title of the second novel and the name Lewis gives to the inhabited Venus-like world. The real planet Venus has an extremely hostile atmosphere, unlike the habitable setting imagined in the book.