Abstract: I will start with an informal introduction to Gromov-Witten invariants which roughly count "curves" passing through given homology cycles. During a joint work with Y.P. Lee, we discovered Gromov-Witten invariants of a projective bundle are uniquely determined by those of the base and the Chern classes. I will briefly talk about our motivation and explain the statements. If there is time, I will also sketch a combinatoric feature of the proof.