Metallic　films　were　widely　used　in　many　micro-cavities　or　as　electrodes.　However,　the　quenching　of　fluorescent　molecules　and　the　large　absorption　loss　of　metallic　films　are　generally　considered　fatal　for　the　lasing.　We　report　the　enhancement　of　amplified　spontaneous　emission　(ASE)　of　organic　gain　media　in　planar　waveguide　structure　with　metallic　film.　Compared　to　the　metal-free　device,　the　ASE　threshold　of　device　with　metallic　film　is　reduced　by　3.7　times　by　introducing　the　spacer　layer　between　metallic　film　and　organic　gain　media.　It　is　found　that　the　radiative　decay　rate,　quantum　yield　of　fluorescent　molecules　and　the　net　gain　of　media　are　enhanced　by　half-cavity　effect　of　Ag　film,　which　lead　to　the　enhanced　ASE　and　lower　lasing　threshold.　(C)　2014　Elsevier　B.V.　All　rights　reserved.