Free　vibration　of　functionally　graded　beams　with　a　through-width　delamination　is　investigated.　It　is　assumed　that　the　material　property　is　varied　in　the　thickness　direction　as　power　law　functions　and　a　single　through-width　delamination　is　located　parallel　to　the　beam　axis.　The　beam　is　subdivided　into　three　regions　and　four　elements.　Governing　equations　of　the　beam　segments　are　derived　based　on　the　Timoshenko　beam　theory　and　the　assumption　of　＇constrained　mode＇.　By　using　the　differential　quadrature　element　method　to　solve　the　eigenvalue　problem　of　ordinary　differential　equations　governing　the　free　vibration,　numerical　results　for　the　natural　frequencies　of　the　beam　are　obtained.　Natural　frequencies　of　delaminated　RIM　beam　with　clamped　ends　are　presented.　Effects　of　parameters　of　the　material　gradients,　the　size　and　location　of　delamination　on　the　natural　frequency　are　examined　in　detail.