The adsorbed state of benzene on the Pd(110)(1X2)-Cs surface at 90 K and its thermal decomposition process in the temperature region up to 650 K have been investigated by using high-resolution electron energy loss spectroscopy, multiplexed thermal desorption spectroscopy, and low-energy electron diffraction. Vibrational spectra show the existence of two chemisorbed states of benzene on Pd(110)(1X2)-Cs at 90 K. For a small exposure (≲0.3 langmuir, fractional coverage θC6H6 ≲ 0.07), benzene is predominantly adsorbed away from the Cs adatoms. With increasing exposure, the adsorbed benzene located near the Cs adatoms is formed additionally. The saturation coverage corresponds to 0.2 C6H6 molecule per Pd atom of the unreconstructed Pd(110) surface (θC6H6 = 0.2). For large exposure (>0.3 langmuir), a part of the adsorbed benzene is desorbed intact at about 300 and 330 K. The thermal decomposition of C6H6 occurs above 300 K, and the CxHy species (x = 1 or ≥3, y = 0, 1) and H atoms are formed on the surface. Only carbon adatoms remain on the Pd(110)(1X2)-Cs surface by heating to 650 K. These results are compared with those for the Pd(110) clean surface, and the effect of Cs adatoms on the surface reactions are discussed.