The men "confessed to having participated actively in the kidnapping of the Chibok schoolgirls," police commissioner Damian Chukwu told journalists on Wednesday in the northern town of Maiduguri, once a Boko Haram stronghold.
The eight men were among a group of 22 fighters arrested within the past two weeks, according to Chukwu.
One of the men, aged 23, "confessed to being one of the Boko Haram commanders who coordinated and led the kidnapping" of the Chibok girls, Chukwu added.
Police said those arrested also admitted to organising more than 50 suicide bombings.
The kidnapping of the Chibok girls captured the world's attention, with celebrities and prominent personalities such as former US first lady Michelle Obama joining a "Bring Back Our Girls" campaign to free them.
Some 2,000 girls and boys have been abducted by Boko Haram since 2014, with many used as sex slaves, fighters and even suicide bombers, according to Amnesty International.
The armed group, which has been active since 2009, wants to enforce a strict interpretation of Islamic law in Nigeria, as well as in bordering regions of Cameroon, Chad and Niger.
Some 20,000 people have been killed and about 2.3 million displaced since Boko Haram started its armed campaign in 2009.