A theoretical and experimental investigation has been carried out into the transient response characteristics of the two-phase condensing flow in a double-pipe condenser. A two-phase two-fluid model, together with the constitutive relations, describes the dynamic behavior of the condensing flow. A semi-implicit finite difference scheme has been employed to solve the governing equations. The flow surge response in the condensate outlet flow to changes in (1) inlet pressure, (2) inlet vapor flow and (3) coolant flowrate are analyzed. The results are presented to show that the transient response of the condensing flow is very sensitive to changes in the condensing pressure. The response to change in the coolant side is relatively slow, due to the thermal capacity of the tube wall. Experimental data are presented which reveal the oscillatory characteristics of the resulting condensing flow transient due to changes in the coolant flowrate. This phenomenon has been well-interpreted by the present analysis.