The human rights group urged authorities to disclose immediately the whereabouts of Hada, who like many Mongolians goes by a single name, and his wife Xinna and son Uiles. They reportedly have been held in an unknown location for at least 10 days by the Inner Mongolian Public Security Bureau.
"China is using enforced disappearance to keep activists and their family members out of the spotlight while the world's attention is focused on China's first Nobel Peace Prize winner, Liu Xiaobo," said Catherine Baber, Amnesty International's Asia-Pacific deputy director.
Hada was scheduled for release Friday after 15 years in prison for "splittism" and "espionage" for his involvement in the Southern Mongolian Democratic Alliance.
His wife and son were arrested Dec. 4 and their family bookstore raided. Their family was told Xinna was held on suspicion of running an illegal business, and Uiles was accused of drug-dealing.
A Mongolian rights group said Hada's sister-in-law, Naraa, got an anonymous CD of photographs of the three eating together, dated Dec. 10.