Shear　keys　as　sacrificial　components　are　widely　used　in　cap　beams　and　abutments　of　highway　bridges　to　limit　the　transverse　displacement　of　superstructures　and　avoid　damage　of　substructures.　To　investigate　the　seismic　capacity　of　bridge　exterior　shear　keys,　six　exterior　shear　key　specimens　were　designed　on　the　basis　of　current　Chinese　seismic　design　guidelines　of　highway　bridges　and　subsequently　tested　under　monotonic　lateral　loading.　The　influence　of　vertical　and　horizontal　reinforcement　ratios　on　the　seismic　capacity　of　the　bridge　shear　keys　was　studied.　Two　typical　failure　modes　of　the　exterior　shear　key　specimens,　diagonal　tension　failure　and　sliding　shear　failure,　were　observed　during　the　tests.　The　reinforcement　ratios　of　the　shear　key　and　cap　beam　have　significant　influence　on　the　seismic　capacity　of　exterior　shear　keys.　Moreover,　different　analytical　models　corresponding　to　the　two　failure　modes　were　developed　to　predict　the　seismic　capacity　of　the　shear　key　specimens　in　this　paper.　Compared　with　the　experimental　results,　the　two　analytical　models　proposed　in　this　study　can　better　predict　the　load-carrying　capacity　of　the　shear　key　specimens　than　the　classical　analytical　models.　(C)　2016　American　Society　of　Civil　Engineers.