There are twe problems involved in the C1 chemisorption on the GaAs (110) surface, one is whether Cl adsorbs on the relaxed surface or on the unrelaxed one, while the other is whether Cl bonded with the surface anion or with the cation. The present work indicates that the Cl atom adsorbs on the relaxed GaAs (110) surface and is bonded with the surface As. The density of states calculated from this configuration seems to agree well with existing experimental results.