After the death of Cedric Diggory and the rumour the dark Lord come back. Ernie is one of the person who believed Harry Potter. In this fifth year, he become a perfect Hufflepuff along with Hannah Abbott

The Ministry get their hands in Hogwarts, Dolores Umbridge being a professor of D.A.D.A and change all the progress. With her presence and the cruel detention, most of students stand up, Ernie joined the Dumbledore's army to fight against her.