Based on the equivalence principle and the reciprocity theorem, the problem of electromagnetic scattering from two adjacent objects is considered and a solution that accounts for multiple scattering up to second-order is evaluated. In general, the first-order solution can easily be obtained by calculating the scatted field from isolated targets when illuminated by a plane-wave. However, due to the difficulty in formulating the coupled scattering field, it is impossible to find an exact analytical solution for the second-order scattered field. In this work, the second-order solution of electromagnetic scattering from two adjacent conducting/dielectric objects is derived by employing the reciprocity theorem and this solution is simplified from volume integral to surface integral form by using the equivalence principle. Meanwhile, the relation between the secondary scattering field from one target and the other is derived. Finally, the composite scattering field from two adjacent spheres is calculated using the formulas obtained in this work. The bistatic scattering pattern is discussed and the results are compared with numerical computations based on Time Domain Integral Equation Method (TDIEM).