It details a daily regimen of humiliation, torture, violence and degradation.
It said that in five years, as many as 13,000 people - majority civilians believed to be opposed to the government - were hanged in secret at the jail.
The Amnesty report is based on interviews with 84 witnesses, including guards, detainees, and judges.
The new report provides further evidence of mass killings in Syrian government prisons, and what it calls the government's "extermination policies". "This was normal for me then".
"We demand that the Syrian authorities immediately cease extrajudicial executions and torture and inhuman treatment at Saydnaya Prison and in all other government prisons across Syria". VOA also emailed the Syrian Foreign Ministry, but to no avail.
The 48-page report claims Syria secretly carried out mass hangings at the Saydnaya Military Prison to eliminate those who spoke out against the government. Detainees included doctors, lawyers, activists, engineers and humanitarian workers, says Amnesty.
Victims would hang for 10 to 15 minutes. "Some didn't die because they are light", he said. Hours later, blindfolded, severely beaten and with nooses around their necks, they would realize their true fate. After being charged with crimes against humanity and given a three-minute trial, prisoners were sentenced to death. Those whose names are called out were told they would be transferred to civilian prisons in Syria. Instead, they were tortured until they gave false confessions.
In addition to the mass hangings, the report includes horrific accounts of torture and abuse suffered in the prison. The group says it's likely thousands more detainees have been killed in the previous year.
"For me, as president, when I do my duty, the same for the government and for the army, to defend our country, we don't look to this issue, we don't care about it", he said. "They would then ask a bigger prisoner to rape him.No one will admit this happened to them, but it happened so often.Sometimes psychological pain is worse than physical pain, and the people who were forced to do this were never the same again". She says upcoming peace talks can not ignore the findings, and calls for Iran and Russian Federation, the regime's closest allies, to push for an end to Syria's "murderous detention policies".
"We believe these practices are known about and approved by the highest level of the Syrian government", Waldman told Fox News.
"The worldwide community, notably the UN Security Council, must act immediately to end the crimes taking place in Saydnaya and other detention centres and ensure that investigations are conducted into who is responsible and that the perpetrators are brought to justice in fair trials".