What is the last book in The Chronicles of Narnia series?

The last book in The Chronicles of Narnia series is The Last Battle.

Written by C. S. Lewis and illustrated by Pauline Baynes, The Last Battle was published in 1956 as the seventh and final Narnia novel. It brings the fictional world's long history to its conclusion, following events roughly two hundred Narnian years after The Silver Chair. The story centers on King Tirian and a crisis caused by the ape Shift, who disguises the donkey Puzzle as Aslan.

The title refers to the conflict that erupts as false religious claims, Calormene intervention, and the defense of Narnia collide. The book ultimately moves beyond a military defeat: Aslan ends the old Narnian world, while the faithful enter a deeper and more perfect “true” Narnia.

Readers sometimes confuse final publication order with internal chronology. The Magician's Nephew is earlier in Narnia's history, but it was published sixth. The Last Battle remains the seventh book by publication order and the series finale. It won the Carnegie Medal in 1957.