A novel microstrip leaky-wave antenna (MLWA) under the operation of the fundamental leaky-wave EH0 mode in a microstrip line (MSL) is presented. Different from the conventional EH0-mode (quasi-TEM) structure with beta/k(0 )> 1, the proposed EH0-mode MLWA is implemented by periodically loading inductive shorting pins along the MSL to excite an EH0 mode fast-wave region with beta/k(0) < 1 for radiation. Herein, both the antenna structure and feeding line are simultaneously excited under the operation of the same EH0 mode, leading to the mode purity with simplified feeding mechanism. Most importantly, the proposed leaky-wave EH0 mode is not restricted by transverse resonant condition of higher-order modes, resulting to realize an arbitrary fast-wave region by virtue of varied periodicity of shorting pins.