The company said in a statement that women and girls made up more than 60% of Australian TikTok users, with 1.5 million using the app, an increase of 380,000 since the second half of 2019.
The data was collected from single-source interviews with 8000 Australians aged above 14 and 1000 interviews with Australians aged between 6 and 13, between January and June.
There were 985,000 male users, up 470,000 since the end of 2019, with use by males growing faster.
Among Australians in older groups, use of the app tended to drop off, with only 9% of millennials (463,000) and 4% of generation X (177,000) using the social media app.
Roy Morgan said the 6-13 age group was the biggest user of social media and 2.1 million (80%) used some form of these apps, with YouTube seeing the most use (1.9 million in an average four-week period).
However, the company pointed out that there was no need to register to use YouTube, while other social sites like Instagram and TikTok required registration.
Roy Morgan said that looking at the generation alpha figures a little closer revealed that 523,000 (39%) of 10-13-year-olds used TikTok, compared to 223,000 of 6-9-year-olds.
Roy Morgan chief executive Michele Levine said: "Australia's 'digital natives' born this century have grown up surrounded by powerful and frictionless technology as the norm and have taken quickly to TikTok. The highest rate of usage is for 'tweens' aged 10-13 years old with nearly 40% on TikTok and teens aged 14-17 years old with almost 30% on the platform.
"Among generation alpha, TikTok is far more widely used than the well-known Instagram, Facebook and Pinterest. Only the ubiquitous YouTube is more widely used and the videos on YouTube are more readily accessible without the need for signing up for an account."
Oracle has now struck a deal to buy TikTok's American operations, but it looks like it will go through only after the 3 November US presidential election.