Forces allied with Libya's unity government said on December 5 that they had ousted IS from the coastal city.
"Libyan authorities should ensure the safety of and urgently provide medical care for more than 120 women and children being held in a Misrata prison" on suspicion of jihadist links, it said.
Forces allied with Libya's unity government said on December 5 that they had ousted IS from the coastal city, 450 kilometres (280 miles) east of Tripoli, after seven months of fighting.
The jihadists had seized Sirte, the hometown of slain dictator Moamer Kadhafi, in June 2015 amid the chaos following Kadhafi's downfall in 2011.
After evacuating the city, Libyan authorities detained a number of civilians suspected of IS links, fears heightened by cases where women blew themselves up after leaving the city.
HRW said authorities have "an obligation to ensure the well-being and security of the women and children" and should not detain them on the basis of suspected relationships to IS fighters.
It cited a prison official who said none of the women had identification documents and another who said some of the women appeared to have been abducted by IS.
HRW urged the government to work with the United Nations and aid agencies to "find safe destinations for those detained and treat them for injuries, illness, and malnourishment".