HRW said the police, known as Carabineros, "committed serious human rights violations, including excessive use of force in the streets and abuses in detention," during the protests.
The New York-based rights group had received hundreds of disturbing reports of abuse, including cases of beatings and sexual assault, Jose Miguel Vivanco, HRW's director for the Americas, told a press conference in Santiago.
"We believe that the abuses are not isolated cases, they are not coincidences," said Vivanco.
The rights groups said in a statement it met with President Sebastian Pinera in Santiago on Tuesday, recommending a series of reforms to help prevent police misconduct.
Watch: Chilean security forces 'intentionally' attacked protesters to 'punish' them
The reforms were needed "in the wake of compelling evidence of excessive use of force and abuses against demonstrators and bystanders."
Among its recommendations is a thorough reform of the Chilean police, including reviewing detention protocols for identity checks, setting up internal control mechanisms and strengthening police training.
"We recognise the value of the Human Rights Watch report and the recommendations that have been made to us," said Lorena Recabarren, the Chilean minister with responsibility for human rights.
She said the findings "concern us and, of course, are ones we receive with pain."
HRW said the police, known as Carabineros, "committed serious human rights violations, including excessive use of force in the streets and abuses in detention," during the protests