We optically characterize a micrometric radio frequency electro-optic modulator based on a lithium niobate photonic crystal. With the vertically deposited sidewalls electrodes, the experimental results show a half-wave voltage length product $V_{\pi }{}^* L$ figure of merit of 0.0063 V-cm, a bandwidth of $\sim 1$ GHz for an active interaction area of $\sim 37$ $\mu$ m $^{2}$ . This is the smallest figure of merit measured on an electro-optic modulator to date by several orders of magnitude with respect to bulk lithium niobate.