The protesters decried the legislators' move as immoral and demanded they slash their salaries by half rather than lifting them by 25 percent to 1.09 million shillings ($13,370) a month.
Already among the best-paid in the world, some MPs say the fact that their salaries are about to be taxed justifies the speedily debated increase.
"Public service should not be for selfish gains. Ninety percent of them are only serving themselves. They have to reduce their salaries by 50 percent and pay tax as any other citizen," Bamgi Ndolo of the Civil Society Congress told Reuters.
Many Kenyans are furious their MPs have voted to adopt a report that would hike their own salaries at a time poorly paid public workers like teachers are clamoring for better pay and east Africa's largest economy recovers from the global downturn.
Their new monthly salary would far outstrip the country's GDP per capita of 57,887 shillings ($708) per year.
As the boisterous but peaceful protesters — fewer in numbers than the demonstration's organizers had hoped for — chanted "thieves" outside Parliament, police had to escort some parliamentarians into the assembly building.
Normally, the next step would be for Finance Minister Uhuru Kenyatta to incorporate the proposed rise into a bill to be passed by parliament.
Kenyatta, however, has already criticized the increase and said there is no provision for such a raise in the 2010/11 budget. But analysts say the legislators could blackmail him by refusing to pass his budget until they get their way.
Critics of Kenya's lawmakers point to live coverage of parliamentary proceedings, which at times shows a distracted assembly.
"Some people are working hard, earning less than 250 shillings per day. The politicians want to put the tax of these people into their accounts while we can see them sleeping in the chambers," said one protester, Emily Achieng.