Around 10,000 people were detained after widespread anti-government protests last month.
Dozens of protesters in Kazakhstan were beaten and tortured by the authorities after last month's unrest, according to Human Rights Watch (HRW).
The NGO said Kazakh security forces had "arbitrarily arrested" peaceful protesters and denied them access to lawyers.
"Police ... subjected some detainees to ill-treatment and torture, including with electric shocks and beatings with batons," HRW said in a statement.
Kazakh authorities have stated that nearly 10,000 people were detained across the country in connection with January’s protests.
Demonstrations initially broke out over a rise in oil prices but later descended into unprecedented, wider anger about living conditions in the former Soviet country.
At least 227 people were also killed in the riots, which saw the country's influential former president Nursultan Nazarbayev ousted from positions of power.
Opposition activist Asset Abichev told AFP that he was arrested on a bus by police, held without charge and tortured for a week.
"They beat me on my chest with their fists, they beat me on my back and arms with a stick and a rifle butt," he said.
"[Young men] had plastic bags put over their heads, they were thrown to the ground, jumped on," Abichev added. "They had broken ribs, but received no medical attention"
According to Kazakh prosecutors, nearly 900 of those arrested face various criminal charges, including mass rioting and acts of terrorism.
Many of those released have stated on social media that they were beaten and tortured by the authorities during their detention.
Hugh Williamson, Europe and Central Asia director at Human Rights Watch, said the reports of torture was "cause for deep concern".
“Kazakh authorities should immediately put a stop to the abuses, ensure that every detainee’s rights are protected, and bring to justice those who beat or tortured them.”
President Kassym-Jomart Tokayev said last week that Kazakh human rights officials were investigating complaints from detainees.
Tokayev has blamed the unrest on "terrorists" and foreign-trained "bandits" but has not provided any evidence to support his claims.
During the riots, the President ordered police to "shoot to kill" and also called in support from Russian-led alliance troops.