The 40 year old's shares in several Portuguese firms, including a TV cable company, and an Angolan bank put her on the billionaires' list, Forbes said.
Her first venture was a restaurant in Luanda called Miami Beach, said the magazine that tracks the world's rich.
Most of the population in oil-rich Angola live on about $2 (£1.25) a day.
Angola is striving to tackle the physical, social and political legacy of a 27-year civil war that ravaged the country after independence from Portugal.
The conflict ended in 2002 and Angola has since emerged as one of Africa's leading oil producers and fastest-growing economies.
The family of President Jose Eduardo Dos Santos - who has been in power for 33 years - controls a large chunk of that economy.
"When you tease out the ownership and controlling interests in Angola it reads like a Who's Who of family members and party and military chiefs," Peter Lewis, an African studies professor at Johns Hopkins University in the US, told Forbes.
Correspondents say Ms dos Santos is a relatively shy public figure despite her successful business career.
Since setting up her restaurant in the capital, Luanda, in 1997 she has become an influential businesswoman in Angola and Portugal.
With a 28.8% stake in Zon, she sits on the Portuguese media company's board and is its largest shareholder, Forbes said.
She also sits on the board of Angola's Banco BIC and is reported to have a 25% share of the bank, the magazine reported.
-BBC
