Polyhydroxyalkanoates　(PHA)　production　by　halophilic　mixed　microbial　cultures　(MMCs)　draw　a　lot　of　attention　because　of　great　advantages,　such　as　free　sterilization,　easily　extraction　and　high　production.　In　this　study,　halophilic　MMC　was　used　to　investigate　the　effect　of　pH　on　PHA　production　in　the　mixed　VFAs　fermentation　process.　The　results　indicated　that　there　was　no　significant　influence　on　PHA　production　in　the　pH　range　of　6.5-8.2.　PHA　production　rate　and　substrate　utilization　rate　would　be　inhibited　in　lower　or　higher　pH　conditions.　PHA　yield　was　influenced　by　pH　in　the　systems,　but　different　influencing　mechanism　existed　in　acidic　condition　and　alkaline　condition.　Alkaline　environment　led　to　higher　dissociation　degree　of　VFAs.　Then　more　energy　needed　as　substrates　being　absorbed,　which　further　led　to　the　decrease　of　VFAs　absorption　rate.　This　affect　was　obvious　when　pH　raised　to　9.2.　Molecular-state　VFAs　changed　intracellular　pH　in　the　acidic　condition.　Then,　the　lower　activity　of　related　enzymes　and　protein　resulted　in　slower　substrate　utilization.　Energy　consumption　of　substrate　utilization　and　microbial　metabolism　reduced　when　pH=5.2,　resulting　in　the　decrease　of　intracellular　PHA　degradation　and　the　increase　of　PHA　yield.　The　pH　value　had　little　influence　on　PHA　component.　And　HV　accounted　for　34.9%-38.3%　of　PHA　weight　when　the　initial　pH　between　5.2　and　10.2.　This　study　would　be　a　guide　for　PHA　production　using　mixed　VFAs　as　carbon　source　by　halophilic　MMCs.　©　All　Right　Reserved.