To　suppress　uncertainties　caused　by　parametric　variations　or　disturbances,　an　adaptive　switching　gain　(ASG)　is　proposed　for　integral　sliding　mode　control　(ISMC)　to　regulate　speed　in　permanent　magnet　synchronous　motors　(PMSMs).　According　to　system　uncertainties,　the　ASG　is　designed　to　adjust　the　switching　gain　to　suppress　the　chattering.　The　adaptive　law　is　a　positive　value　resulting　in　an　increment　of　the　switching　gain　when　the　tracking　trajectory　is　outside　the　boundary　layer.　Conversely,　it　is　negative　with　a　decrement　of　the　gain.　Further,　it　improves　a　convergent　rate　by　the　function　of　the　reciprocal　of　the　tracking　error　when　the　trajectory　enters　the　sliding　phase.　ISMC　with　the　ASG　is　applied　to　a　PMSM　experiment　with　the　result　that　this　method　can　effectively　suppress　high　frequency　chattering　and　shows　excellent　steady　state　performance　of　the　current　loop　and　speed　in　a　servo　system.