Kardashian, who announced her pregnancy last month, revealed the baby's sex in a Father's Day post on Instagram showing West with the couple's daughter, North, who turned 2 last week.
"Precious moments like this when we were traveling on tour with you are what I live for," the 34-year-old reality TV star wrote along. "You're such a good daddy to North & you will be the best daddy to our new son too!"
Kardashian also shared the news on Twitter:
E! reported earlier this month that the baby is due in December.