We study the asymptotic form of the Gopakumar-Vafa invariants at all genera for Calabi-Yau toric threefolds which have the structure of fibration of the A n singularity over P 1 . We claim that the asymptotic form is the inverse Laplace transform of the corresponding instanton amplitude in the prepotential of N = 2 SU (n + 1) gauge theory coupled to external graviphoton fields, which is given by the logarithm of the Nekrasov's partition function.