The　objective　of　the　current　paper　is　to　develop　a　simple　hand　formula　to　estimate　the　fundamental　vibration　period　of　tall　buildings　for　use　in　equivalent　lateral　force　analysis　specified　in　building　codes.　The　method　based　on　the　Sturm-Liouville　differential　equation　is　presented　here　for　estimating　the　fundamental　period　of　natural　vibration.　The　resulting　equation,　based　on　the　continuum　representation　of　a　tall　building　braced　by　coupled　shear　walls　for　natural　vibration　of　the　building,　is　proved　to　be　the　fourth-order　Sturm-Liouville　differential　equation,　and　a　hand　method　for　determining　the　fundamental　period　of　natural　vibration　of　the　building　is　presented.　Making　use　of　the　coupled　wall　theory　for　natural　vibration,　the　method　is　extended　to　deal　with　the　vibration　problem　of　other　tall　buildings　braced　by　frame,　walls　and/or　tube.　The　method　has　the　merit　of　being　simple　in　terms　of　numerical　computation　and　presentation　and　yet　is　very　versatile　when　combined　with　numerical　analysis.　Once　the　structural　parameters　α　H　and　μ　of　a　tall　building　are　computed,　the　fundamental　vibration　period　of　the　building　can　be　readily　obtained.　The　value　of　the　method　is　that　it　will　allow　a　more　consistent　and　accurate　use　of　code　formulae　for　calculating　the　earthquake-induced　maximum　base　shear　in　a　tall　building.　Use　of　the　method　is　economical　with　respect　to　both　computer　time　and　equipment,　for　example　a　hand　calculator　would　suffice　to　handle　the　calculations　of　period　of　the　buildings　at　concept　design　stage.　It　can　also　be　useful　to　verify　the　results　of　the　finite-element　method　where　the　time-consuming　procedure　of　handling　all　the　data　can　always　be　a　source　of　errors.