The announcement, made in a statement and at a meeting of the Global Polio Eradication Initiative in New York yesterday, leaves just two countries - Pakistan and Afghanistan - on the list.
In declaring Nigeria "no longer polio endemic", the WHO said: "This is the first time that Nigeria has interrupted transmission of wild (naturally occurring) poliovirus, bringing the country and the African region closer than ever to being certified polio-free."
Countries have to go at least 12 months without a case before they can be considered for removal from the list while polio-free status comes after three years without a case.
The WHO said "all laboratory data have confirmed a full 12 months have passed without any new cases".
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The announcement is the latest good news in the global battle against the virus, which is spread by poor sanitation and contaminated water and can cause irreversible paralysis.
Children under-five are particularly vulnerable.
On August 12, Africa marked one year since the last recorded case of polio - in Somalia - raising hopes of its elimination across the continent.
In 2015, 41 cases of wild poliovirus have been reported worldwide - 32 in Pakistan and nine in Afghanistan.