Overall, the number of new cases fell by 21 percent between 2010 and 2015, and mortality rates fell by 29 percent -- 31 percent in the African region.
But globally there were still 212 million new cases and 429,000 deaths last year, and 43 percent of the population in sub-Saharan Africa were not protected by treated nets or indoor spraying.
The WHO warned that "sustained and sufficient funding for malaria control is a serious challenge", saying that after a steep increase between 2000 and 2010, investment had "flat-lined".
"In 2015, malaria funding totalled $2.9 billion, representing only 45 percent of the funding milestone for 2020 ($6.4 billion)," it said.
The United States provided about 35 percent of all malaria funding in 2015, while governments of countries with malaria provided about 32 percent, and Britain provided 16 percent.
"We are definitely seeing progress," said Dr Pedro Alonso, director of the WHO Global Malaria Programme, ahead of the report's launch in London.
"But the world is still struggling to achieve the high levels of programme coverage that are needed to beat this disease."
Resistance to anti-malarial drugs is also a challenge, as is growing mosquito resistance to insecticides, the report said.
The WHO however highlighted improvements in sub-Saharan Africa over the past year in providing help for pregnant women and children against malaria.
"Malaria-related deaths among children under five in sub-Saharan Africa are at their lowest point in history," said Ray Chambers, the UN Secretary-General's special envoy for malaria.
"This is largely attributable to the nearly 500 million insecticide-treated bed nets delivered over the past three years, the highest ever, along with significant expansion of diagnosis and treatment."
Deaths from malaria among the under fives globally have fallen by 69 percent since 2000 to 303,000 last year.
Sub-Saharan Africa was home to 90 percent of global malarial cases and 92 percent of deaths.
"We must now not grow complacent, but drive forward to end the epidemic once and for all," said Chambers.