Combining　phase-transition　materials　with　optical　microcavities　may　advance　the　applications　of　whispering-gallery　mode　(WGM)　lasing　in　performance　customization,　sensing,　and　optical　switching.　In　this　study,　switchable　WGM　lasing　based　on　phase　transition　is　reported.　The　device　is　designed　by　introducing　the　phase-transition　hydrogel　into　the　capillary　microcavity.　After　approaching　the　phase-transition　point　in　hydrogel,　the　number　of　WGM　lasing　modes　decreases　sharply　with　a　significant　blueshift　in　the　wavelength.　The　phenomenon　is　caused　by　the　increase　in　light　scattering　and　decrease　in　effective　refractive　index　of　the　device.　Furthermore,　single-mode　lasing　is　obtained　by　manipulating　the　phase　transition,　which　exhibits　superior　reversibility.　This　study　may　pave　the　way　for　designing　and　multifunctioning　of　novel　WGM　lasing　in　photonic　devices.　©　2023　Optica　Publishing　Group.