This article presents an EH0-mode microstrip leaky-wave antenna (LWA) with enhanced gain in broadside by bidirectionally exciting the inductive-loaded EH0-mode microstrip line (MSL). In this way, enhanced gain is successfully attained in broadside at the desired frequency. To theoretically investigate such an attractive property, an equivalent circuit model is first established to illustrate that the working frequency as well as the phase and leakage constants can be independently controlled by altering the shunt inductance and resistance, and further properly adjusting their quantities. Then, a row of shorting pins is appropriately loaded at one side of the MSL, so as to realize the inductive-loaded periodical leaky-wave structure for broadside radiation. After that, a more effective and practical transmission line model is derived to fully investigate the side pin-loaded MSL. Based on this transmission line model, an efficient method is proposed to design the working frequency and the values of $\beta /k-{0}$ and $\alpha /k-{0}$ in a controllable way. Furthermore, a gain enhancement of such an LWA is carried out with resorting to the directivity and radiation efficiency, aiming to acquire the maximum antenna gain. In final, the proposed EH0-mode LWA with broadside radiation is simulated, fabricated, and measured. Good agreement can be found between the simulated far-field radiation patterns and the tested ones, which both evidently indicate that a high-gain broadside radiation beam is indeed achieved at the desired frequency.