Transition　metal　selenides　nanoparticles/carbon　composites　have　been　one　of　the　promising　lithium/sodium　ion　battery　anodes.　In　the　present　study,　NiSex　nanoparticles　encapsulated　into　microporous　flowerlike　carbon　have　been　prepared　by　a　hydrothermal　route　directed　by　the　flowerlike　Ni/C　composite　template.　In　a　low　hydrothermal　temperature　(i.e.,　120 °C),　the　metallic　Ni　nanoparticles　are　transformed　into　Ni0.85Se,　which　has　an　average　particle　size　of　~　13.02 nm.　The　selenization　degree　and　particle　size　can　be　obviously　improved　at　a　higher　hydrothermal　temperature　(i.e.,　160　or　180 °C),　accompanying　with　the　decrease　in　carbon　content,　and　partial　Ni0.85Se　nanoparticles　have　been　transformed　into　NiSe2.　As　anode　of　lithium　ion　batteries,　the　NiSex　obtained　at　180 °C　(i.e.,　180 °C-NiSe)　can　deliver　a　higher　discharge　capacity　(e.g.,　851.0 mA h g−1　after　100　cycles　at　0.2 A g−1)　and　better　cycling　stability　compared　with　the　low　temperature　obtained　sample.　However,　the　rate　capability　and　sodium　ion　storage　performance　of　120 °C-Ni0.85Se　are　better　than　the　180 °C-NiSex,　and　a　discharge　capacity　of　326.5 mA h g−1　can　be　reached　at　a　high　rate　of　5 A g−1　for　120 °C-Ni0.85Se.　Also,　a　high　capacity　retention　ratio　of　64.3%　after　100　cycles　can　be　reached　for　120 °C-Ni0.85Se　as　sodium　ion　battery　anode.　The　different　electrochemical　performance　can　be　attributed　to　the　decreased　particle　size.　©　2019,　Springer　Science+Business　Media,　LLC,　part　of　Springer　Nature.