Williams, 37, said she rarely came across black dolls when she was growing up and wanted to make sure her baby had one.
Serena Williams says she made sure the first doll her daughter Alexis Olympia received was Black, and her second one will be white as she teaches a message of "love for each other."
"Qai Qai is a doll I got for her. I wanted her to have a black doll," she said after easing into the tournament second round Tuesday. "Growing up, I didn't have that many opportunities to have black dolls. And I was just thinking, like, I want her first doll to be black.
"And her heritage, obviously she's mixed, she's Caucasian and black, but I feel like that was her first doll and I said her second doll would be Caucasian. "I definitely want to always teach her love and teach her just that humans should always have love for each other, no matter what color they are," she added.
Bizarrely, the doll has its own Instagram page with more than 87,000 followers, and growing. Qai Qai is described on the social media platform as "daughter and best friend of @olympiaohanian and granddaughter of @serenawilliams."
Williams said the name Qai Qai came from her nephew.
"We were all sitting in our living room, and we were running around names, and he said, 'call her Qai Qai'. He actually is the magic behind the name," said the American.
The tennis great, in Melbourne in her bid to win a 24th Grand Slam title, is married to Reddit co-founder Alexis Ohanian with their first child born in late 2017.
Williams last played the Australian Open in 2017, when she won the tournament while eight weeks pregnant. She assured reporters she wasn't expecting again as she reflected on life on the road with a child.
"It's definitely different to travel with a toddler as opposed to a baby, an infant," she said. "Infants I think are easier, and everyone said it's easier. I didn't quite understand. Olympia takes a lot more attention now, which is why I'm trying to get out of here (press conference room). It's cool. It's really cool to be a mom and to be her mom, in particular. I feel really special."