Despite　recent　advances　have　been　made　in　clinical　treatments　of　breast　cancer,　the　general　prognosis　of　patients　remains　poor.　Therefore,　it　is　imperative　to　develop　a　more　effective　therapeutic　strategy.　Lysine　demethylase　4B　(KDM4B)　has　been　reported　to　participate　in　breast　cancer　development　recently,　but　its　exact　biological　role　in　breast　cancer　remains　unclear.　Here,　we　observed　that　KDM4B　was　down-regulated　in　human　primary　BRCA　tissues　and　the　low　levels　of　KDM4B　expression　were　correlated　with　poor　survival.　Gain-　and　loss-of-function　experiments　showed　that　KDM4B　inhibited　the　proliferation　and　metastasis　of　breast　cancer　cells.　Besides,　knockdown　of　KDM4B　promoted　the　epithelial-mesenchymal　transition　(EMT)　and　cell　stemness　in　breast　cancer　cells.　Mechanistically,　KDM4B　down-regulates　PHGDH　by　decreasing　the　enrichment　of　H3K36me3　on　the　promoter　region　of　PHGDH.　Knockdown　of　PHGDH　could　significantly　reversed　proliferation,　migration,　EMT,　and　cell　stemness　induced　by　KDM4B　silencing　in　breast　cancer　cells.　Collectively,　we　propose　a　model　for　a　KDM4B/PHGDH　axis　that　provides　novel　insight　into　breast　cancer　development,　which　may　serve　as　a　potential　factor　for　predicting　prognosis　and　a　therapeutic　target　for　breast　cancer.