A 91-year-old letter written by Sergeant Harry Michael Dean, who later married and raised a family in Port Kembla, was found tucked inside a Bible donated for the Lifeline South Coast Book Fair next month.

Volunteer Mabel Symons, of Balgownie, said she was surprised to open the Bible and find the single-page letter.

"I looked at the letter and saw the date - June 15, 1917 - and thought, 'that's very interesting'," she said.

Lifeline South Coast warehouse manager Rochelle Wilson said the letter had been addressed to a cousin, Mr Taylor of Epping, before making its way to the Illawarra.

At the time, Sgt Dean, 27, was recuperating in an English hospital after having his leg amputated after a German raid at Messines Ridge in France.

"Just a few lines to say I was wounded on Easter Monday at Hill 60 when Fritz came over on a raid and dropped a bomb at my feet," he wrote.

"Was lying in a trench before found by own infantry, for a period of about 20 hours - the longest 20 hours ever spent.

"At No 10 Casualty Clearing Station, Tuesday midnight, had left leg taken off below the knee."

Mrs Wilson said research had shown Sgt Dean was a highly qualified mining engineer before joining the war effort with the 1st Australian Tunnelling Company.

He married his wife, Helen, five months after his return to Australia in 1918 and began a long career as a metallurgical chemist at Port Kembla.

He died in April 1961 at Port Kembla.

Mrs Symons said it was hoped the owner of the letter would come forward. Otherwise, the Australia War Memorial would add the missive to its collection.

A volunteer with Lifeline for 31 years, Mrs Symons said many unusual items had been found inside books over the years, including century-old photographs and postcards.

The next Lifeline South Coast Book Fair will be held at Kembla Grange Racecourse on September 5-7 and will feature more than 50,000 books for sale.

Donations can be made at Lifeline's Wollongong or Unanderra outlets or any Lifeline collection bin.

To become a volunteer at the fair or for information, call 4228 0722.