Kate and Gerry, who are Catholics, are being joined for the service by a war memorial in their home village of Rothley, Leicestershire by loved ones and supporters.
Madeleine's great uncle Brian Kennedy, who is attending the service, was quoted by the Daily Star as saying: "We find it hard to believe eleven years have passed but we never lose hope.
"We've no idea how many might turn up after such a long time but all are welcome.''
Madeleine was three-years-old when she vanished in Praia de Luz, in the southwestern Algarve region of Portugal on 3rd May 2007.
A police investigation to try and find the youngster has cost more than £11 million.
In a message left on the official Find Madeleine Campaign page on Facebook, Kate and Gerry said: "It gets harder to know what to say or write as each anniversary of Madeleine's abduction approaches then passes.
"Life is full and busy which helps but Madeleine is still missing and she is still dearly missed.
"Information continues to come in (incredible as it may seem after so long, although we are grateful for that) and work goes on.
"Perseverance and hope remain."