The New York-based group said riot police had on several occasions used "what appears to be excessive force to disperse largely peaceful protesters at a series of demonstrations".
"There is no justification for attacking peaceful protesters," said Eric Goldstein, deputy Middle East director at HRW.
"The authorities should show they will not tolerate abuses by investigating all allegations of abuse by security forces and punishing those responsible for violating rights."
During large demonstrations staged by the opposition since October 15, police frequently used tear gas and stun grenades and beat up protesters, leading to the injury of dozens and the arrest of many more, said HRW.
Commenting on the report, Kuwait's information ministry said that law enforcement authorities intervened only when protests grew violent and endangered public and private property.
"Kuwait has witnessed several protests in 2012 where streets were blocked and riots took place at residential areas, endangering civilian and public property," said the ministry in a statement sent to AFP.
"Law enforcement authorities are required to maintain law and order and ... to protect the right of the people to civic services," read the statement, which said violent demonstrations were "illegal."
It recalled that authorities had allowed several processions to take place this year after organisers obtained a proper licence and police provided necessary protection to protesters.
The Islamist, nationalist and liberal opposition, angry over an amended electoral law, has been staging protests almost every night since December 1 polls to demand the parliament's dissolution and scrapping of the amendment.
The parliament, described as totally pro-government, has however begun normal business after it was inaugurated by Emir Sheikh Sabah al-Ahmad Al-Sabah on December 16.
"Kuwait's rulers need to fully respect the right to assemble peacefully," Goldstein said. "Declaring a gathering 'unauthorised' does not give police licence to beat protesters."