Vomit or spit up? Small amounts of spit up are pretty normal. If it's actual vomiting it could be reflux or if you're formula feeding you could be over feeding. Either way, if it's a large amount of vomit on a regular basis I'd speak with the baby's doctor about it, they can prescribe medicine or a specific formula for babies with reflux.
You can help the HubPages community highlight top quality content by ranking this answer up or down.