The　extreme　halophilic　archaeon　Haloferax　mediterranei　can　produce　polyhydroxyalkanoates　(PHAs)　and　extracellular　polymeric　substances　(EPSs)　simultaneously.　In　this　study,　we　studied　the　influence　of　the　ratio　of　carbon　and　nitrogen　concentration　(C/N)　during　feeding　on　PHA　and　EPS　production　in　open　fermentation　by　means　of　the　developed　model.　The　results　indicated　that　nitrogen　availability　had　significant　effects　on　stain　growth　and　PHA　and　EPS　synthesis.　The　PHA　volumetric　productivity,　EPS　volumetric　productivity　and　biomass　increased　with　the　increase　of　nitrogen　concentration.　Haloferax　mediterranei　synthesized　EPSs　with　a　faster　rate　than　that　for　PHAs,　indicating　that　EPSs　were　synthesized　as　priority　energy　and　food　reserves　by　Haloferax　mediterranei.　The　deficiency　of　nitrogen　promoted　PHA　accumulation.　The　highest　PHA　cell　content　of　47.22%　mg　PHA　per　mg　CDW　was　found　at　a　C/N　ratio　of　35.　In　contrast,　the　highest　EPS　productivity　of　733.58　mg　L-1　was　observed　at　a　C/N　ratio　of　5.　At　a　C/N　ratio　of　35,　the　percentage　of　the　PHA　yield　coefficient　in　the　sum　of　the　PHA　and　EPS　yield　coefficient　was　92.8%,　indicating　that　the　majority　of　the　carbon　was　converted　to　PHA　rather　than　EPS.　Supported　by　the　carbon　flow　and　PHA　and　EPS　productivity,　PHA　was　the　main　product　of　Haloferax　mediterranei　despite　the　C/N　ratio.　The　study　proved　that　controlling　the　C/N　ratio　during　feeding　could　be　one　solution　to　adjust　the　carbon　flow　to　PHA　and　EPS　synthesis　by　Haloferax　mediterranei.