This　paper　demonstrates　the　optically　induced　self-excited　relaxation　oscillation　in　a　silicon　ring　resonator　for　the　first　time.　The　observed　thermo-optomechanical　oscillation　has　a　unique　waveform　with　fast　oscillation　period　close　to　16　ns　and　slow　oscillation　period　approximately　167　ns.　The　ultra-fast　oscillation　period　can　be　well　used　in　optical　switch　and　optical　memory　elements.　Particularly,　the　oscillation　frequency　is　very　sensitive　to　the　wavelength　detuning,　making　it　quite　suitable　for　the　sensing　applications.