The star was to be in Europe to promote the release of her new disc and for the premier of her new movie in London.
A statement from Jen said: "I very much wanted to be in London today but unfortunately I’m not well. At the advice of my doctors I’m unable to travel."
The 35 year old star added, "Being sick has also caused me to cancel my European album tour. Please accept my sincerest apologies as I have to remain in Los Angeles."
Lopez was to be in London for the opening of her movie Shall We Dance, with co-star Richard Gere. The movie opens there on Friday.
The new CD of the singer, Rebirth will be in stores in the beginning of March.