The development comes on the day that Chinese President Xi Jinping is to start his first summit with President Barack Obama in California.
Chen Guangfu now plans to travel to Taiwan to meet his brother, who now lives in the US after his dramatic escape from house arrest last year, which infuriated Chinese authorities.
A diplomatic stand-off ensued for several weeks until the lawyer was allowed to leave the country.
"We received (the passports) by post, there was no reason stated for why they arrived now," he said.
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"Guangcheng will go to Taiwan on June 23... If possible we will travel to Taiwan to meet him and his family."
His son Chen Kegui, who was sentenced to jail last year for assaulting a police officer in what rights groups said was a reprisal for Chen Guangcheng's escape, told him last month that he was in "great pain" with continued appendicitis, he added.
Obama has been pressed to raise human rights issues during his meetings with Xi, including the plight of Chen Guangcheng's family.