A　theoretical　analyzing　approach　about　a　class　of　seismic　isolation　systems,　RFPS　(Rolling　Friction　Pendulum　System),　is　presented.　It　starts　from　the　relative　kinematics　energy　theorem　in　multiply　body　dynamics.　This　system　consists　of　two　rollers　placed　in　the　vicinity　of　two　circular　concave　curve　slides　to　form　the　non-indented　contacts.　Computational　results　shows　that　it　has　the　essential　capabilities　required　for　an　effective　isolation　system.　The　rather　long　vibration　period　provides　the　necessary　isolation　capability,　the　gravity　provides　the　reposition　capability,　and　the　rolling　friction　acting　at　the　contacting　surface　on　the　top　and　bottom　plate　respectively,　provides　the　energy　dissipation　capability.　The　inter-storey　drift　resulting　from　seismic　action　could　be　drastically　decreased　on　buildings　equipped　with　a　RFPS　system.　If　an　optimum　combination　of　slide　radius　and　a　rolling　friction　coefficient　is　adopted,　the　seismic　isolation　effect　could　be　as　high　as　90%.　When　the　slide　radius　is　in　the　range　of　2　m-3　m　and　the　rolling　friction　coefficient　less　than　0.01,　the　RFPS　system　posses　good　energy　dissipation　and　reposition　capability.