Recent figures show 20% of women science graduates in Wales go on to work in the subject versus 44% of men.
Another study shows women account for 35% of UK PhD science graduates, but only 11% of senior lecturers and 8% of professors.
The Soapbox Science event runs 13:00-16:00 BST on Saturday at the city centre's Alliance sculpture.
The 12 scientists, many of them experts in their field, will tells passersby about their specialism and their passion for science.
Organisers said now was a "time of great opportunity for budding female scientists", pointing to an average annual shortfall of 40,000 new science, technology, engineering and mathematics skilled workers in the UK.
Soapbox Science, which is on a month-long national tour, will be in Swansea on 8 July.
The Cardiff event, on The Hayes, ran for the first time last year, attracting 1,000 people.
In March, a report said only one in six workers in key sectors in Wales is a woman and only 12% of engineering and technology students are female, calling it a "a waste of knowledge and talent".
Women researchers will get on their soapboxes at a Cardiff event to promote women in science.