Can I bring ancient books from Hong Kong to the Mainland?

You can't. According to the introduction of the mainland's entry policy for China and Hong Kong, ancient books from China and Hong Kong are not allowed to be brought into the mainland. Ancient books are important cultural relics, which are not allowed to enter the country. Hong Kong, China (hereinafter referred to as "Hong Kong") The China Special Administrative Region (hereinafter referred to as "Hong Kong") is located in the south of China, bordering the Pearl River Estuary in the east, China and Macau across the sea in the west, Shenzhen in the north and Wanshan Islands in Zhuhai in the south. Its regional scope includes Hong Kong Island, Kowloon, New Territories and 262 surrounding islands.