Lithium niobate (LN)-based modulators offer superior modulation performances, including high-speed modulation, linearity, and temperature stability. However, these devices exhibit larger sizes due to the low light-matter interaction despite a significant electro-optic coefficient. In this work, we present a compact LN-based modulator using a plasmonic mode that confines the optical mode in a very narrow gap. By filling the gap with LN, the confinement factor in the LN is significantly enhanced. The proposed modulator provides an extremely small half-wave voltage-length product, VπL of 0.02 V/cm at an optical communication wavelength (λ = 1.55 µm). The proposed modulator scheme can be utilized in a wide range of optical communication devices that demand small footprints and a high-speed operation.