A　copper　microscratch　test　was　carried　out　with　a　spherical　indenter　under　constant　normal　load　of　150　mN.　The　effect　of　sample　tilt　on　the　measurement　of　friction　coefficient　was　investigated　by　rotating　the　sample　with　surface　inclination　between　successive　tests　so　that　the　indenter　could　experience　different　surface　height　slopes.　It　was　found　that　the　experimentally　measured　friction　coefficients　linearly　depended　on　surface　height　slope　(or　surface　tilt　angle)　under　small　angle　tilt　and　became　larger　when　the　indenter　climbed　over　the　sample　surface,　which　was　explained　by　a　geometrical　intersection　model.　Accurate　determination　of　the　friction　coefficient　requires　either　two　scratch　tests　with　reversed　sliding　directions　or　180　degrees　rotation　of　the　sample　with　the　average　value　being　used　as　the　coefficient　of　friction　under　nontilting　condition.　The　true　friction　angle　for　the　condition　without　surface　inclination　can　be　obtained　by　summing　the　experimentally　measured　friction　angle　and　surface　tilt　angle.