Sessions court judge Mohamed Saman Ramli said the sexual acts, captured on closed circuit television, appeared voluntary "just like husband and wife."
He said neither woman pushed the constable away or screamed, there was no medical evidence of bruises, the women were married, had children, and voluntarily took their clothes off.
Constable Razali Pilen, 25, was charged with raping a 23-year-old Filipino and a 24-year-old Indonesian, held as illegal immigrants, in February.
Four women’s groups — All Women’s Action Society, Sisters In Islam, Women’s Aid Organisation and the Women’s Candidacy Initiative — condemned the judge’s "insensititive comments" and said he failed to consider the element of fear and intimidation.
"It is highly disturbing when a learned person does not understand the dynamics of rape or rape victims, and with the bias, decides the fate of women," they said in a joint statement.
"We are also disheartened that the rape myth is still well and alive and being perpetuated by the very authorities involved in the carrying out of justice," the statement added.
The fact that the women were illegal immigrants should not affect the trial but help the judge understand the degree of compliance on their part, they said.
"We, and certainly women in Malaysia, need to have our faith restored that our criminal justice system is just and fair. Otherwise victims of sexual assault will continue to be silenced and denied justice," it said.
Rights group Suaram said the "callous judgement" could encourage similar violations and "give a carte blanche to police officers to abuse their position and authority."
Attorney General Abdul Gani Patail has instructed his officers to file an appeal in the High Court against the verdict.
Razali’s case comes against the background of an outcry in the Philippines over the alleged rape by Malaysian police of a 13-year-old migrant girl ahead of her deportation in a recent crackdown on illegal immigrants.
President Arroyo wrote to Prime Minister Mahathir Mohamad earlier this month to express her "personal outrage and that of the Filipino people" over the alleged rape.
Mahathir pledged swift action over Arroyo’s complaint.