A 1958 edition of Philosopher Zhang Dainian's An Outline of Chinese Philosophy is one of book collector Feng Kechen's favorites among his collection of secondhand books.

Feng is an engineer of Nokia China Research Center in Beijing and a book-addict who spends nearly every weekend he has free browsing the used bookstores around town.

He has been collecting secondhand books since 1991, his passion fired by the purchase of a copy of the periodical Reading first published by SDX Joint Publishing Company in 1979.

Feng is planning to send his An Outline of Chinese Philosophy to Tsinghua University, as he has discovered that the university's Zhang Dainian archive does not yet include the book.

As Feng says, one of the joys of collecting secondhand books is being able to share them with other book lovers, as the value of books lies in using and reading it.

"Like Feng Kechen, most gold-seekers at secondhand book markets belong to the frontline of intellectuals, aged from 30 to 50. A love of reading is their hallmark, said Hu Bin, who is better known as Hu Tong, who founded Booyee.com.cn in 2004 - one of first online secondhand book stores in China.

Many factors such as author, contents, publishing date, times of printing, and historical significance contribute to a book's desirability as a collectable, and to its price.

The original price tag is no longer a judgment of a book. A book with a price tag of 0.5 yuan may be worth hundreds of yuan, while some best-selling books tagged at scores of yuan commonly sell at 1 yuan on the secondhand market.

However, a highly sought after and prized used book can be priced as high as thousands of yuan.

One book in Hu's collection, is just such a treasure, the book is not intrinsically valuable, its worth comes from this particular copy's history: it was read by Xu Xiangqian on the road of the Long March, and has inscriptions on flyleaves and notes in margins.

However, such treasures are not something you come across every day. Because of the small number of good used books, used book dealers find it hard to stay in business and secondhand book fairs are shrinking. Wudaokou's used book market moved to a smaller one near Beihang University in 2001 and disappeared in 2006.There is only one regular used book market in town.

Price increases are another factor. "Before 2001, secondhand books were usually charged at 0.01yuan per spread. The development of the Internet, and the increasing online demand for such books, has pushed their prices up to a point, where they now range from 5 yuan to 400 or 500 yuan."

But Beijing is still a vibrant secondhand wonderland, thanks to its long history, and the fact it houses the largest number of institutions, universities and research centers in China.