Foreign envoys based in Thailand such as the Chinese and Bangladeshi ambassadors appeared at the embassy this morning to sign the book, as well as a group of Buddhist monks.
The Cambodian embassy has opened compound for the book signing every day this week between 9.30am and noon and again from 2-4pm, through Friday.
The embassy lowered the Cambodian flag to half-mast to mourn for the late revered monarch, who was called 'King-Father' by many of his people.
The Thai authorities have deployed police to facilitate traffic in the area.
The Cambodian ex-monarch died on Monday of a heart attack in Beijing at the age of 89. He reigned from 1941 to 1955 and again from 1993 until his voluntary abdication on Oct 7, 2004 in favour of his son, the current King Norodom Sihamoni.
His Majesty King Bhumibol Adulyadej sent condolences to Cambodia's King Norodom Sihamoni over the loss of his father.
Prime Minister Yingluck Shinawatra also sent a message to her counterpart Prime Minister Hun Sen, saying the Thai government shared the feeling of loss with the Cambodian people.