Abstract: Jordan’s lemma can be used for a wider range than the original one. The extended Jordan’s lemma can be described as follows. Let f(z) be analytic in the upper half of the z plane (Imz≥0), with the exception of a finite number of isolated singularities, and for P>0, if =0 where z=Re^iφ and CR is the open semicircle in the upper half of the z plane.With the extended Jordan’s lemma one can find that Laplace transform and Fourier transform are a pair of integral transforms which relate to each other.