The pages contain four "dirty jokes" and an explanation of sex, contraception and prostitution, the ABC reports, which were covered with gummed pieces of brown paper when the diary was first found - presumably Anne's attempt to hide her risqué writing from her family.
The previously unknown writing was discovered behind brown paper that covers up two pages in Frank's diary.
In an interview, Ronald Leopold, executive director of the Anne Frank House, said, "It is really interesting and adds meaning to our understanding of the diary".
The young Jew, then aged 13, and her family had only been in hiding from the Nazis in Amsterdam for two months.
The pages contain jokes, similar anecdotes also appearing elsewhere in the diary, and Anne's view of sexual education. The passages show how she "creates a fictional situation that makes it easier for her to address the sensitive topics that she writes about", he said.
The Huygens Institute of Netherlands History was also a partner in the project.
The researchers used digital photography techniques to decipher pages that Anne had masked with glued brown paper some time after writing them on September 23, 1942.
With regards to prostitution, she wrote: All men, if they are normal, go with women, women like that accost them on the street and then they go together. The Frank family lived in a modest brick building from 1934 in the Dutch capital, after fleeing rising anti-Semitism in neighbouring Germany, until they went into hiding.
VIDEO: Anne Frank Though German Jewish teenager Anne Frank did not survive the Holocaust, the memoirs from her two years in hiding live on forever. "Papa has been there".
Leopold and a senior researcher on the project, Peter de Bruijn, both expressed to the Times the value of the uncovered diary pages for offering more insight into Anne Frank's development as a writer rather than for the content she wrote about. The family went into hiding in July 1942 and remained there, provided with food and other essentials by a close-knit group of helpers, until August 4, 1944, when they were discovered and ultimately deported to Auschwitz.
After the war, Otto Frank had his daughter's diary published, and it went on to become a symbol of hope and resilience that has been translated into dozens of languages. Anne Frank and her sister Margot died at Bergen-Belsen in 1945.