"Small children and older readers alike will be delighted by its subversive touches, and they will be entertained by its warmth and fun."
Unka, who wrote and illustrated the book, was praised for its design and wide-ranging appeal.
"We think The Boring Book will help cultivate a love of words and books," Mrs Else said. "It combines beautiful production and perfect design, which seamlessly integrates the words and text. It's refreshing on so many levels."
Unka took home $15,000 for her awards.
Books by well-known Kiwi authors Joy Cowley and Elizabeth Knox were also recognised in the annual awards, with Cowley's Dunger topping the Best Junior Fiction category and Knox's Mortal Fire the Young Adult fiction category.
Mrs Else described Dunger as a "quintessentially New Zealand story, the characters are believable in themselves and in how they relate to the other members of the family ... Best of all, the novel is not in the least politically correct."
Knox and Cowley scooped $7500 each in prize money.
Debut writer Rachel Stedman won the Best First Book Award for A Necklace of Souls, and the Children's Choice for the evening went to Yvonne Morrison and Donovan Bixley's The Three Bears ... Sort Of.
Prize money for each of the categories was $2000.
"This year's winners are remarkable pieces of work," Mrs Else said. "These authors are champions. We're particularly excited by the visual appeal of the titles."
NZ Post book awards
*The Boring Book by Vasanti Unka. New Zealand Post Margaret Mahy Book of the Year and winner of Best Picture Book category.
*The Beginner's Guide to Hunting and Fishing in New Zealand by Paul Adamson. Best Non-Fiction.
*Dunger by Joy Cowley. Best Junior Fiction category winner.
*Mortal Fire by Elizabeth Knox. Best Young Adult Fiction winner.
*A Necklace of Souls by Rachel Stedman. Best First Book.
*The Three Bears ... Sort Of by Yvonne Morrison and Donovan Bixley. Children's Choice category winner.
*Bugs by Whiti Hereaka. Honour award.
*Taka Ki Ro Wai by Keri Kaa and Martin Page. Maori Language award.