Researchers acknowledge the science behind how extra weight is linked to cancer is not clear - but say hormones produced by extra fat may play a part.
They say more studies are needed.
`Wake-up call`
Around 9,000 women are diagnosed with womb cancer in the UK each year and around 2,000 women die from the disease.
Researchers say treatments have improved over the last 20 years - mirrored by better chances of survival.
But they call for more research to understand why a greater number of women are getting the disease.
Prof Jonathan Lederman, at Cancer Research UK, said: "It is worrying that womb cancer cases are going up so sharply.
"We don`t know all the reasons why, but we do know that about a third of cases are linked to being overweight - so it is no surprise to see the increases in womb cancer cases echo rising obesity levels."
It`s not clear exactly what causes womb cancer, but certain things can increase the risk of developing the condition.
Experts say extra fat may produce hormones and growth factor molecules that encourage cells to replicate, increasing the chance of tumours forming.
Other factors - such as a lack of exercise, age and genes have all been implicated too.
Kath Bebbington, who is 56 and from Greater Manchester, was diagnosed with womb cancer three years ago and said it prompted her to change her eating and exercise habits.
She added: "My cancer diagnosis was a wake-up call for me. It was a shock because I don`t smoke, I don`t drink and I walk a lot.
"And we don`t know what caused the cancer but I had to admit to myself that I needed to make some lifestyle changes to lose some extra pounds I had been carrying and stack the odds in my favour for a healthy future."
Dr Alison Tedstone, chief nutritionist at Public Health England, said: "We know that being overweight or obese increases our risk of some cancers which is why it`s important to keep an eye on portion sizes and cut back on calories, sugar and fat in the diet."
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