Abstract: An equivalent circuit for receiving antennas, which is composed of open-circuit voltage source and radiation impedance, is derived rigorously from electromagnetic boundary conditions based both on reciprocity theorem and the concept of reaction. The parameters of the equivalent circuit are related to the selected current distribution reacted with the electric field. Illuminated by the numerical example of a dipole, it shows that the equivalent circuit with open-circuit voltage source has a clear physical meaning and it is more suitable in the analysis of receiving systems.