We　report　a　plasmonic　Fabry-Perot　(F-P)　microcavity　with　silver　nanoparticles　and　a　continuous　silver　film　function　as　the　end　mirrors,　where　the　silver　nanoparticles　were　produced　through　photo-reduction.　Filled　with　a　layer　of　light-emitting　polymer,　the　F-P　microcavity　becomes　an　active　device　with　its　output　spectrum　dependent　on　localized　surface　plasmon　resonance　(LSPR)　of　silver　nanoparticles.　A　phase　shift　as　large　as　pi　is　resolved　in　the　resonance　modes　of　the　F-P　microcavity　due　to　the　modulation　by　LSPR.　This　leads　to　complementary　spectroscopic　performance　in　the　output　of　the　plasmonic　microcavity　with　respect　to　its　non-plasmonic　counterparts.　(C)　2015　Optical　Society　of　America