The　effect　of　cavity　structures　on　the　tuning　properties　of　polymer　lasers　was　investigated　in　two　common　distributed-feedback　cavities.　The　configurations　of　the　two　cavities　are　substrate/grating/active　waveguide　and　substrate/active　waveguide/grating,　respectively.　The　polymer　lasers　were　operated　in　the　liquid　environment,　and　the　laser　wavelength　was　tuned　dynamically　by　changing　the　refractive　index　of　the　liquid.　Polymer　lasers　based　on　the　substrate/grating/active　waveguide　structure　showed　a　higher　tunability　than　those　based　on　the　substrate/active　waveguide/grating　structure　due　to　a　larger　electric　field　distribution　of　the　laser　mode　in　the　liquid　environment.　It　is　expected　that　these　results　will　be　useful　in　the　development　of　tunable　laser　sources.