Campaigning "has been marred by violence targeting women" despite early warnings and government pledges to tackle the issue, the International Federation for Human Rights (FIDH) and the Kenya Human Rights Commission (KHRC) said.
They said several rape cases, including four incidents following a botched campaign rally in the east of the capital Nairobi in June, have been reported.
"The failure by the government to curb the targeting of women in politics and to hold perpetrators accountable... has enabled repeat violence," FIDH vice-president Sheila Muwanga said.
Violence -- including sexual violence -- continues to cast a shadow over elections in Kenya, which will vote for a new president, MPs and other representatives on Tuesday.
There is no woman running for the top job but three of the four candidates have female running mates.
The rights watchdogs said women candidates faced aggressive sexist language, gender stereotyping, online abuse and harassment, including sexual overtures.
"These tactics are consciously deployed to prevent women politicians or candidates from participating in active politics," they said, calling attention to previous elections that saw high levels of sexual violence.
Months of politically motivated inter-ethnic violence convulsed Kenya following a disputed presidential election in 2007.
More than 1,100 people were killed, with at least 900 people suffering sexual assaults according to rights groups.
The 2017 presidential vote was also followed by widespread violence against women and girls, according to the Kenya National Commission on Human Rights who documented 201 election-related sexual and gender based assaults.
More than half the attacks implicated security agents and "to date no action has been taken by the government to ensure justice for the victims," FIDH and KHRC said.
UN experts last month urged Kenyan authorities to "ensure women can participate freely in the electoral process, without discrimination, harassment or fear of potential repetition of sexual and gender-based violence."
In 2020, a Nairobi court ordered the government to pay compensation to four women who suffered sexual violence in the aftermath of the 2007 vote.