The report -- "Keep Your Head Down: Unprotected Migrants in South Africa" -- says foreign migrants endure both extortion and assault at the hands of many South Africans.
"Police, immigration officials and military border patrols in South Africa often seriously abuse undocumented migrants when they arrest them," said Georgette Gagnon, HRW deputy Africa director.
Commercial farmers allegedly violate South Africa's immigration law by hiring undocumented workers and paying them below the mandated minimum wage.
Gagnon called on the government to revamp immigration laws to better support migrants.
"The government should ensure that its officials comply with procedures for arrest, detention and deportation set out in the immigration law," Gagnon said. "It should also introduce a system for undocumented migrants to report abuses, and it should investigate, prosecute and discipline officials who violate the law."