The 32-year-old reality star has revealed that she is just nine weeks into her second pregnancy.
Kourtney and partner Scott Disick, 28, already have a son Mason, who turns two on December 14.
Surprise! Kourtney Kardashian has revealed she is pregnant with her second child
Little bump ahead: Kourtney covered up her form with a billowing dress on a date with boyfriend Scott Disick earlier this week
Kourtney first revealed the news to this week's issue of Us Weekly.
And Kourtney was so excited, she couldn't wait the traditional amount of time before sharing it with the world.
Announcement: The reality star broke the news on the cover of Us Weekly today
In an episode of Keeping Up With the Kardashians in July, Kourtney was seen clashing with mother Kris Jenner after she mentioned that she and Scott were considering trying for another baby.
While their first child Mason was a happy surprise, the family matriarch is adamant that the couple should be married before thinking about expanding their family.
New sibling: The couple are already parents to adorable Mason, who turns two next month
Kourtney and Scott have broken up a number of times over Kourtney's disapproval of her partner's hard partying and anger issues.
During their stint in Miami last year, Kourtney ordered Disick to leave her and their son alone after he turned violent and smashed a mirror, telling him 'I love Mason more than I love you.'
Scott has since worked out his issues and has said he has no problem marrying his long-time love.
Feeling good: Kourtney, who is just nine weeks along, was in high spirits yesterday as she shopped in LA
Turning down his offer of marriage during dinner on their four-and-a-half year anniversary in April, Kourtney asked, 'Things are so good right now, why would we want to change that?'
And headstrong Kourtney has clearly decided not to fulfil her mother's wishes to get married before falling pregnant again.
'It wasn't like we weren't trying,' Disick says. 'We kind of just said, "If it's meant to be, it'll be.'"
Growing brood: Mason's arrival in 2009 was a happy surprise for the couple, who have been together on and off for almost five years
The 30-year-old, who recently separated from husband Kris Humphries after just 72 days, said in a magazine interview this week that she feels her dreams of children may be dashed.
‘At first I was like, I want six kids. Then I went down to four, then I was down to three, and now I'm like, maybe I won't have any.’
Defiant: Kourtney clashed with mother Kris Jenner earlier this year over not wanting to get married before having another baby
No wedding bells: Kourtney has said she has no plans to marry until she's sure her children won't have to go through a divorce the way she did
‘Maybe my fairy tale has a different ending than I dreamed it would.’
Today, Kourtney's sister Kim tweeted her excitement at the happy news.
'This is such a blessing and the whole family is beyond thrilled!' she wrote. 'I just know Mason will make the best big brother and I can’t wait to meet my new little niece or nephew!
'Congratulations Kourtney and Scott. Xo'
Excited: Kim Kardashian tweeted her congratulations to her older sister today
Speaking on The Today Show last month, the 27-year-old admitted: 'It's so hard. I never knew about ovulation and the limited amount of time that you have to get pregnant.
'I never knew about that. No-one ever taught me that.'
For the full interview, buy Us Weekly, on US newsstands today or visit UsWeekly.com
Baby race: Both of Kourtney's sisters Kim and Khloé have spoken publicly in recent weeks about their dreams of having children and fears it may not happen