A　diamond　sphere　of　radius　105　mu　m　was　used　to　slide　on　fused　silica　under　ramping　load　from　5　mN　to　5　N　in　order　to　investigate　scratch-induced　deformation　and　micro-cracking　of　brittle　solids.　Complete　circular　cracks　were　observed　with　elastic　deformation　playing　the　predominant　role.　Results　show:　initial　cracking　can　be　detected　by　acoustic　emission;　the　valleys　of　horizontal　mean　contact　pressure　and　the　apparent　friction　coefficient　together　with　the　sudden　rise　of　the　ratio　of　vertical　work　over　horizontal　work　indicate　the　beginning　stage　of　circular　cracks;　micro-comminution　is　signified　by　the　decrease　in　residual　depth.　Values　of　fracture　toughness　obtained　by　Vickers　hardness　techniques　are　larger　than　reasonable　ones.　Scratch-based　approaches　by　linear　elastic　fracture　mechanics　and　microscopic　energetic　size　effect　laws　are　found　to　be　applicable　to　assess　fracture　toughness　of　brittle　glass　by　scratch　test　with　a　spherical　indenter　under　an　appropriate　range　for　curve　fitting.　Fracture　toughness　of　fused　silica　measured　by　scratch　test　is　0.7　MPa.m(1/2),　which　is　compared　favorably　with　the　values　obtained　by　conventional　methods.