The　seismic　vulnerability　of　single　pylon　cable-stayed　bridges　under　strong　ground　motions　in　the　transverse　direction　is　of　great　concern　to　earthquake　engineering　researchers　and　bridge　engineers.　Introduction　of　base　isolation　to　cable-stayed　bridges　has　been　proved　very　effective　in　reducing　seismic　forces　in　the　bridges　in　previous　studies.　This　paper　proposes　a　direct　displacement　based　seismic　design　(DDBD)　procedure　for　base　isolated　cable-stayed　bridge　under　transverse　seismic　excitation.　One　of　the　key　aspects　of　the　DDBD　is　the　realization　of　a　uniform　transverse　target　displacement　of　the　deck　under　seismic　excitation,　which　is　achieved　by　appropriate　design　of　the　isolator　stiffness　at　the　bottom　of　the　pylon　and　the　ends　of　the　deck.　The　proposed　DDBD　procedure　is　applied　in　this　paper　to　the　seismic　design　of　a　single　pylon　cable-stayed　bridge　isolated　by　friction　pendulum　bearings.　The　effectiveness　and　the　accuracy　of　the　resulting　design　are　checked　by　nonlinear　time　history　analyses.　The　numerical　results　indicate　that　the　proposed　DDBD　procedure　can　predict　the　deck　displacement　profile　and　amplitudes,　as　well　as　the　base　shear　within　a　reasonable　degree　of　accuracy.　The　case　study　demonstrates　that　the　proposed　DDBD　procedure　is　sufficiently　accurate　and　practical　for　the　seismic　design　of　base　isolated　single　pylon　cable-stayed　bridges.