Ai Takagi, 23, pleaded guilty to four of seven sedition charges lodged against her and her Singaporean husband, Yang Kaiheng, 27.
The three other charges, as well as an additional charge of withholding information from the police, will be taken into consideration during her sentencing on March 23.
Yang, however, is claiming trial.
Both were based in Australia but arrested in February last year during a visit to Singapore. They are currently out on bail.
Takagi, described by prosecutors as the owner and chief editor of the now defunct site 'The Real Singapore', was teary-eyed as a statement of facts in the case was being read in court.
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The site was forced to close by the media regulator last year for playing up articles seen as fomenting racial hatred.
Immigration has been a hot-button issue in Singapore in recent years.
Yang and Takagi were also charged with withholding from police information on the website's advertising revenues, which were estimated at A$459,604 (Sg$473,000) over a 17-month period.
Court documents showed its Facebook page had more than 400,000 likes, while the site itself had almost 13 million views a month.
At a district court on Tuesday, Takagi pleaded guilty to fabricating two articles attacking Filipinos and another targeting mainland Chinese.
They included an article which said that a Filipino family instigated a fracas at a Hindu festival, and another alleging that a Chinese woman made her grandson urinate into a bottle inside a metro train.
These articles tended to "promote feelings of ill-will and hostility" between different races and between Singaporeans and foreigners working in the city-state, court documents said.
Singapore's sedition laws make it an offence to promote hostility between different races or classes in the multiracial city-state, which is mainly ethnic Chinese.
About 40 percent of the labour-starved island's 5.5 million people are foreigners.
Each sedition charge carries a penalty of up to three years in jail and a maximum fine of A$4850, or both.
They also face one month in jail and up to A$1,450 in fines, or both, for withholding information from police.
Last September, Filipino nurse Ello Ed Mundsel Bello was jailed for four months for sedition after insulting Singaporeans online and calling on his countrymen to take over the city-state.
In 2009, a local Christian couple, Ong Kian Cheong and Dorothy Chan, were jailed for eight weeks each for distributing and possessing anti-Muslim and anti-Catholic publications.
