In this paper a recent new quasi-TEM surface impedance approach has been applied to fast characterization of multiconductor microstrip lines in terms of inductance and resistance matrices and conductor losses. Application examples for frequency-dependent parameters of interconnect circuits with up to five conductors (three-, four-, and five-strips) have been reported. The propagation characteristics and attenuation of multimode symmetrical multiconductor system are obtained. The effectiveness of the applied approach is confirmed by comparison of the computed numerical results with those obtained by full-wave simulators. They are found to be in good agreement.