In this paper, a compact leaky-wave antenna (LWA) using slow-wave half-mode substrate integrated waveguide (SW-HMSIW) and spoof surface plasmon polariton (SSPP) is proposed. The slow-wave effect is introduced by the blind via-holes at the bottom substrate and the periodical slots etched on the top metal layer. The LWA's radiation is subsequently realized by introducing a simple single-sided sinusoidal modulation to the periodic slots on the top metal layer. Owing to the slow-wave structure, the proposed LWA has a compact size (3.65λ0× 0.4λ0× 0.03λ0). Within the operating bandwidth 8.9-9.5 GHz, the simulated scanning range is from 4° to 78° with the simulated realized gain all above 6.5 dBi.