Guided-wave characteristics of planar periodic microstrip lines with inductive loading are investigated by resorting to the unitlength transmission parameters of an equivalent transmission line. By applying the SOC de-embedding technique, the above two quantities are effectively extracted from the full-wave MoM modeling of a microstrip line with finite periodic cells. Extensive results at first confirm the slowwave behavior such that both real parts of such two quantities rise up slowly and then rapidly with frequency. Further, they demonstrate, for the first time, the guided-wave bandstop characteristic with non-zero attenuation constant and imaginary characteristic impedance. Five-cell periodic microstrip circuits are then designed and fabricated for theoretical and experimental verification.