Kourtney, 34, who is already mother to Mason, three, and one-year-old Penelope, has shared the happy news with friends, according to US media reports.
"Kourtney has confessed she is expecting. She is very excited and only telling a select few right now - but she just couldn't keep it quiet any longer," a source said.
Kourtney and Scott had planned to have another baby right after Penelope arrived.
"Kourtney has that kind of glow she had with Mason and Penelope, they wanted to have one right after Penelope. I know Kourtney and Scott have been trying. So a baby now makes sense, it is very easy to get pregnant after giving birth once, let alone twice," the source added.
"She didn't drink during the whole trip," the source said.
Kourtney's sister Kim recently gave birth to a baby girl.