"We started with a batch of 10 prisoners who moved in early in the morning," Correctional Services spokesperson Russel Mamabolo said in Pretoria.
"The numbers will pick up during the day and the rest of the week."
Only maximum security prisoners with no further criminal charges pending against them would be held in the new institution.
Mangaung Maximum Security Prison, designed to house 2 928 inmates, represented a new approach to reduce overcrowding in South African jails, the department said.
A consortium of five companies led by Group 4 built the facility at a cost of R328 million. Group 4 manages similar prisons in the United Kingdom and Australia.
The government will pay the consortium a fixed price per prisoner, in the region of R90 per day.
This will enable the consortium to recover its construction expenses within 15 years.
In terms of the contract, the prison is to become government property after 25 years.
The department said on Monday that Group 4 was responsible for security and for providing inmates with proper accommodation, medical treatment, nutrition, and recreational and rehabilitation programmes.
"A Correctional Services controller, based at the prison, will monitor all activities and ensure that Group 4 complies with the contract," the department said.
Upon their admission, prisoners were placed in an induction programme, which will run for at least two weeks, to be assessed with regard to their needs, interests and aptitudes.
"On the basis of this assessment, a personal development plan will be worked out for each inmate."
The department said this approach was aimed at giving prisoners incentives and opportunities to take responsibility for their own conduct.
They would be allowed time to spend outside their cells, during which inmates would receive educational, industrial and vocational training.
Life-skill classes would form part of the rehabilitation programme.
Prisoners would receive the same privileges as inmates elsewhere in the country. The number of visits and telephone calls they would be entitled to would be determined by the classification of each inmate, the department said.