An analytical methodology for characterizing electrical transitions associated with transmission line-based microwave channels is presented in this paper. The methodology is formulated using ABCD matrixes obtained from S-parameters measured to two lines with different length and terminated with the transition under investigation. This allows to determine the two-port network parameters of the transition in a simple and direct way. Excellent results are obtained when characterizing coplanar waveguide-to-microstrip and coaxial-to-microstrip transitions. Moreover, the methodology was also successfully applied to obtain the network parameters of packages fabricated on printed circuit board technology.