Pamela Anderson visits Wikileaks founder Assange in London prison
Assange is in London's Belmarsh Prison serving a 50-week sentence for jumping bail in 2012. He is also being held on an extradition warrant to the United States for allegedly hacking into a Pentagon computer.
The actress, who has defended Assange before, told reporters on Tuesday that he is innocent and being treated unfairly.
"It was great to see him, but this is just misrule of law in operation. It is absolute shock that he has not been able to get out of his cell," she said.
Prior to being jailed, Assange had been holed up for nearly seven years at the Ecuadorian embassy in London. He first fled to the embassy in the UK capital's plush Knightsbridge district after being accused of sexual assault in Sweden - allegations that have since been dropped.
Ecuador's government withdrew Assange's asylum status in April, citing alleged international convention violations.
Assange says he is a journalist who has done nothing wrong. He is fighting extradition to the US.