The reality TV star and the rapper - who are expecting their first child together - can't go ahead and tie the knot because Kim's divorce from basketball player Kris Humphries hasn't been finalised, so they've reportedly decided to hold a commitment ceremony during which they will declare vows and exchange rings.
A source told The Sun: "Kanye is very traditional. He'd have liked to marry Kim now they are having a baby. But with Kim still married to someone else, there is not much he can do.
"It won't be official like a wedding because Kanye wants that to be extra special when the time comes. But they will still exchange rings - they just won't wear them on their wedding fingers."
The ceremony will apparently take place at a mansion in Malibu.
The insider added that the event would be "a lot more low-key than a wedding".
Kim, 32, and Kanye, 35, announced their news at the beginning of the year. The baby is thought to be due at the end of June and the couple have already started preparing by splashing out on a family home in Bel Air.