We present a self-consistent pseudopotential study of the atomic geometry, electronic states, and chemisorption of ordered one and two monolayers of Sb on III-V(110) surfaces. For the first monolayer the Sb atoms chemisorb most strongly in the epitaxially continued layer structure (ECLS). The calculated interface atomic geometry agrees well with LEED and X-ray standing wave analyses, and the interface states in the bulk band gap agree with recent photoemission data. For ordered two monolayers in the ECLS the interface shows a metal-like density of states in the band gap.