Based　on　the　structure　of　the　full　unit　cell　which　is　formulated　by　three　translational　symmetries,　three　further　180　rotational　symmetries　of　three-dimensional　(3D)　four-directional　braided　composites　are　clarified　in　this　paper.　It　is　for　the　first　time　that　each　rotational　symmetry　is　used　to　reduce　the　full　unit　cell　to　a　half,　quarter,　and　eighth　size.　The　corresponding　boundary　conditions　for　thermal　analysis　are　derived　precisely　according　to　each　rotational　transformation.　The　effective　thermal　conductivities　of　composites　with　different　fiber　volume　fractions　and　interior　braiding　angles　are　calculated　by　the　full,　quarter　and　eighth　unit　cells.　In　order　to　confirm　the　significance　of　accurate　boundary　conditions,　additional　comparison　calculations　with　adiabatic　boundary　conditions　are　conducted　and　the　result　reveals　that　inappropriate　boundary　conditions　may　lead　to　an　un-neglectable　error　in　the　prediction　of　thermal　conduction　behaviours.　The　numerical　model　is　validated　by　good　agreement　between　the　numerical　results　and　the　available　experimental　ones.　(C)　2016　Elsevier　Ltd.　All　rights　reserved.