Philippa Wood, 40, and 17-year-old Cressida Grant, both from Putney in southwest London, are vying for the title of Miss Great Britain 2006.
Previously multiple generations have been barred from entering pageants together because of age restrictions.
However, Miss Great Britain, regularly vilified by feminists, has been relaunched this year without any limits on how old contestants can be.
A-level student Cressida said she was the one who originally wanted to take part in the competition.
"I saw it first on the internet. I clicked on an advert and noticed there were no age limits this time, so I told mum she should enter too."
She added: "Mum is drop dead gorgeous and turns heads wherever she goes.
"I really want to do well but I just suspect mum might get that little bit further."
Former model Philippa said she had never entered a beauty pageant before, but was looking forward it.
"I'm not sure how either of us will do, but we will both be rooting for each other. Hopefully at some point we will be standing on the same stage together.
"It's not going to cause any rivalry, it will be fun."
Fashion entrepreneur Robert de Keyser recently bought the rights to the competition with former winner Liz Fuller, and announced a new format.
Contestants can enter over the internet, and the final in London in February will be judged in Pop Idol style by an audience and text message voting as well as a panel of experts.
Miss Great Britain is the UK's oldest beauty pageant and was first held in 1948.
Mr de Keyser said: "Not only is there no upper age limit but we are happy for mothers and even grandmothers to enter, as long as they are confident they can compete in the beauty stakes - which no doubt Philippa can."