According to Forbes. Osaka raked in $37.4m (£30.7m) in prize money and endorsements over the last year.
The sum was £1.15m more than the amount earned by 23-time Grand Slam singles winner Williams.
Here is more on the same.
The 38-year-old Serena has been the highest paid female athlete for the last four years.
She has earned between $18 million to $29 million.
However, Osaka has now broken Maria Sharapova's previous record for a female athlete which was set in 2015 when she totaled $29.7 million (£24.4m).
Notably, since Forbes began tracking women athletes' income in 1990, tennis players have topped the show.
Osaka came to prominence after winning the 2018 US Open.
She beat Serena in the final to claim her maiden Grand Slam.
Osaka then sealed the season-opening Australian Open in 2019.
She beat Petra Kvitova and took the WTA number one rankings from Simona Halep.
However, her form in the Slams disappeared since then.
She has now dropped to 10th in WTA Rankings.
Osaka's form may have suffered a dent, however, her tryst with sponsors continued to surge.
According to Forbes, Osaka now has 15 endorsement partners and has signed a lucrative apparel deal with sportswear company Nike.
Osaka ranks 29th in the top 100 highest paid athletes, ahead of Serena who sits 33rd.
Forbes' full list for 2020 is expected to be published next week.
Serena, who last won a Grand Slam in 2017, had been the world's highest-paid female athlete in each of the past four years. Prior to that, Sharapova ruled the show for five years.
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