In this paper, a novel class of microstrip leaky-wave antennas (MLWAs) under the operation of the fundamental EH-mode in a microstrip line (MSL) is presented. The leaky-wave 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 free-space counterpart so as to create a fast-wave frequency region for leaky-wave propagation and radiation. Compared with its counterpart higher order EH- or EH-mode MLWAs, the strip width of this EH-mode MLWA can be freely designed with unspecified or narrow strip width. Our extensive investigations are then carried out to demonstrate its inductive-loaded fast-wave 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, with simulated and measured results in good agreement, validating the proposed pin-loaded technique for designs of EH-mode MLWAs.