In September alone there were 38 reported deaths from cholera, said the UN's Office for the Coordination of Humanitarian Affairs (OCHA) in the capital Niamey on its website.
The spike in the number of cholera deaths was due in part of heavy flooding which has inundated Niger since June.
Steps are being taken "to contain the illness" and "prevent it from appearing in new places," said OCHA yesterday, noting that cholera has broken out in four of Niger's eight regions.
Many refugees have settled on the islands of Lake Chad "where access to drinking water is limited and the conditions of hygiene and sanitation are precarious," the UN office said.
Cholera is transmitted by ingesting food or drink contaminated with human waste. It causes diarrhoea, dehydration and death if let untreated.