In this paper, a novel class of microstrip leakywave antennas (MLWAs) under the operation of the fundamental EH0-mode in a microstrip line (MSL) is presented. The leakywave radiation is realized by periodically loading a set of shorting pins in the central plane along the longitudinal direction. Due to the inductive effect of these shorting pins, the phase constant of this pin-loaded MSL is reduced below its freespace counterpart so as to create a fast-wave frequency region for leaky-wave propagation and radiation. Compared with its counterpart higher order EH1- or EH2-mode MLWAs, the strip width of this EH0-mode MLWA can be freely designed with unspecified or narrow strip width. Our extensive investigations are then carried out to demonstrate its inductive-loaded fastwave mechanism and distinctive characteristics, such as narrower strip width, low cutoff frequency, wide single-mode band, and controllable leakage constant in the fast-wave region. In final, two antenna prototypes with strip widths of 4.0 and 7.5 mm are designed, fabricated, and measured.