The Diana, Princess of Wales Memorial Fund expects to wind up in the next seven years, despite its motto "the work continues".
The charity's sister fund in the US is also considering its future as a grant-giver.
The number of grants awarded has fallen since the fund was set up in 1997. In 2002, it gave £12 million, but this figure has fallen to £7 million this year.
Jo Bexley, spokeswoman at the fund, said: "We never intended to be around forever. We are a grant-making trust rather than a fundraising charity, so we exist to spend. The fund prides itself on making large grants."
Although there is no time frame for the fund, it was intended to exist for the generation that knew the Princess and was expected to run for 12-15 years.