The son - who is named Jackson - is the first child for the 36-year-old Oscar winning actress, although no further details have been released.
A representative confirmed: "Charlize has adopted a child. She is the proud mom of a healthy baby boy named Jackson."
Charlize - who split from boyfriend Stuart Townsend in January 2010 after almost nine years together - has previously said she has found it hard to deal with the single life, but now finds it more empowering.
She said: "I don`t think I`ve actually been on a date with somebody I didn`t know. I`ve been on dates with my boyfriend of course but I`ve never really dated.
"I`ve been in serious relationships from the time I was 19 and I`m single for the first time in my life since then. I had to make a real conscious effort to rediscover myself and it`s hard. I`m a creature who has really found her comfort in relationships.
"I`m really at peace and feeling good about it. All of us go through darkness but that doesn`t make you dark. There`s something really powerful in being OK with being alone, especially for women."