It is recognized that higher dimensional spacetime D>4 play an important role in physics. Khuri pointed out several years ago, in nonrelativistic potential scattering with a compact space dimension, that the forward scattering amplitude has nonanalytic behavior under certain circumstance. If such were the case in QFT (with a compact dimension) it will be matter of concerns. We consider a massive, scalar field in flat D=5 dimension and compactify a spatial coordinate on a circle. We study analyticity property of four point amplitude.