"Most of the interest has been in Anne; not much is known about Margot," museum spokeswoman Annemarie Bekker told AFP of the latest project.
"This exhibition will allow people to get to know her (Margot) a little better."
In her diary, Anne Frank chronicled two years of hiding with her family before their capture by the Nazis in August 1944.
The 15-year-old Anne and Margot, 19, died of typhus at the Bergen-Belsen concentration camp in March 1945, just a few weeks before it was liberated by the British Army.
Their mother Edith died at Auschwitz.
'Serene, intelligent and modest'
Bekker said several of Margot's school friends were at the opening of the exhibit on Tuesday, including 85-year-old Jetteke Frijda.
"She described Margot as serene, intelligent and modest," Bekker said. "Anne was extroverted, Margot was the opposite."
Margot is also believed to have kept a diary during the war years, but it was never found.
"Jetteke believes this is a good thing, as Margot would not have wanted her private thoughts exposed to the world," Bekker said.
Items on display include photos and letters, a swimming certificate and rowing medal, and a message Margot wrote in her friend Frijda's diary.
Father Otto Frank was the only one of the eight people hiding in their "Secret Annexe" to survive World War II, editing Anne's diary for publication before he died in 1980 aged 91.
The diary became one of the most renowned accounts of Jews hiding from Nazi persecution and has sold more than 35 million copies in 70 languages.
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