In a structure, the noise source does not always coincide with the origin of excitation. Vibrational energy is transmitted in the structure and noise is radiated from the surface. For noise and vibration control in beam or shell structures, it is important to clearly identify the excitation sources and vibrational energy transmission characteristics. In this paper, measurement of transient vibrational power flow in a car door excited by impact using the envelope vibration Intensity technique is described. Vibrational power flow caused by flexural vibration in the car door panel is measured with the three channel method. The vibrational power flow is expressed with vibration intensity vectors at each measuring point. Instantaneous distributions of measured vibration intensity vectors in the car door panel are shown in this paper. Temporal and spatial variations of the vibrational power flow are discussed.