In　this　study,　GelGreen　(TM)　was　investigated　as　a　replacement　for　SYBR　(R)　Safe　to　stain　DNA　in　cesium　chloride　(CsCI)　density　gradients　for　DNA-stable　isotope　probing　(SIP)　experiments.　Using　environmental　DNA,　the　usage　of　GelGreen　(TM)　was　optimized　for　sensitivity　compared　to　SYBR　(R)　Safe,　its　optimal　concentration,　detection　limit　for　environmental　DNA　and　its　application　in　environmental　DNA-SIP　assay.　Results　showed　that　GelGreen　(TM)　was　more　sensitive　than　SYBR　(R)　Safe,　while　the　optimal　dosage　(15X　concentration)　needed　was　approximately　one-third　of　SYBR　(R)　Safe,　suggesting　that　its　sensitivity　was　three　times　more　superior　than　SYBR　(R)　Safe.　At　these　optimal　parameters,　the　detection　limit　of　Gel-Green　(TM)-stained　environmental　DNA　was　as　low　as　0.2　mu　g,　but　the　usage　of　0.5　mu　g　environmental　DNA　was　recommended　to　produce　a　more　consistent　DNA　band.　In　addition,　a　modified　needle　extraction　procedure　was　developed　to　withdraw　DNA　effectively　by　fractionating　CsCI　density　gradients　into　four　or　five　fractions.　The　successful　application　of　Gel-Green　(TM)　staining　with　C-13-labeled　DNA　from　enriched　activated　sludge　suggests　that　this　stain　was　an　excellent　alternative　of　SYBR　(R)　Safe　in　CsCI　density　gradients　for　DNA-SIP　assays.