In　the　current　study,　a　quasi-3D　model　is　proposed　for　the　free　vibration　and　dynamic　analysis　of　micro-scale　functionally　graded　(FG)　circular　arches　with　various　boundary　conditions.　The　size　effect　is　taken　into　account　in　this　model　by　employing　modified　couple　stress　theory.　To　take　into　account　the　shear　and　stretching　effects,　a　new　quasi-3D　theory,　based　on　the　parabolic　shear　deformation　theory　and　displacement　fields　of　arch　structure,　is　developed.　The　Ritz　method　and　Lagrange　equation　are　adopted　to　derive　the　algebraic　form　governing　equations.　The　dynamic　analysis　of　FG　micro-arches　subjected　to　a　moving　load　is　carried　out　by　using　Newmark　method.　The　size　effect　on　the　free　and　forced　vibration　behaviors　of　FG　micro-arches　are　investigated　via　various　numerical　examples.　The　numerical　results　show　the　size　effect　plays　a　significant　role　in　both　free　and　forced　vibration　behaviors　of　FG　micro-arches.