Sha Tin District Council lost nine members, including chairman Raymond Li – who took part in primary Legco elections last year – and vice-chairman George Wong.
Three members of Tai Po District Council were stripped of their seats, as well as four members of Sai Kung District Council, including Ricky Or – who is being prosecuted over the primary polls.
Or said he had fulfilled his duty to take the oath and would continue to uphold the Basic Law and One Country, Two Systems principle.
A total of 50 councillors had pledged allegiance to the the SAR on October 4. The oath administrator, Home Affairs Secretary Caspar Tsui, questioned the validity of the pledges made by 16 of them and asked them to provide further information.
In a statement, the government said it decided to strip the 16 councillors of their seats after considering their written replies and all the relevant information.
A final batch of councillors, from New Territories West, was to swear allegiance at a ceremony on Friday afternoon.