Particles　with　an　aerodynamic　diameter　of　2.5　mu　m　or　less　(PM2.5)　in　the　ambient　air　are　affected　not　only　by　local　emissions　but　also　by　regional　transport　of　the　pollutant　and　its　precursors,　which　may　vary　considerably　under　different　meteorological　conditions.　This　issue　has　been　extensively　investigated　in　terms　of　the　contribution　of　regional　transport　to　PM2.5　at　different　seasons　in　a　specific　year.　However,　the　literature　yields　conflicting　results,　and　the　extent　to　which　inter-annual　meteorological　variation　affects　the　contribution　of　regional　transport　is　not　fully　understood,　especially　in　the　long-term.　Therefore,　in　this　study,　the　WRF/CMAQ　model　was　employed　to　investigate　inter-annual　variations　in　the　contribution　of　regional　transport　to　PM2.5　concentration　in　Beijing　from　2001　to　2015.　The　emission　inventory　and　model　configurations　were　kept　the　same　for　the　15year　simulation　to　highlight　the　impact　of　inter-annual　meteorological　variations.　The　major　findings　can　be　summarized　as　follows:　(1)　inter-annual　meteorological　variation　has　an　impact　on　both　the　PM2.5　concentration　in　Beijing　and　the　contribution　of　regional　transport;　(2)　the　annual　average　PM2.5　concentrations　in　Beijing　varied　during　the　study　period,　from　75.3　mu　g/m(3)　in　2002　to　108.1　mu　g/m(3)　in　2003;　(3)　the　years　with　high　annual　anomalies　of　PM2.5　was　found　during　periods　of　low　wind　speed,　high　relative　humidity,　and　low　planetary　boundary　layer　(PBL)　height;　(4)　the　annual　variability　was　relatively　small　compared　to　the　changes　in　seasonal　because　some　seasons　in　a　year　are　higher　than　their　historical　average　values,　and　some　are　lower,　which　often　negate　each　other,　making　the　annual　average　close　to　the　historical　average;　(5)　the　contribution　of　regional　transport　averaged　44.5%　and　ranged　from　40.7%　in　2007　to　48.5%　in　2001.　On　a　seasonal　basis,　the　interannual　fluctuation　was　more　significant,　with　fluctuation　rates　of　43.0%,　25.5%,　25.0%,　and　20.6%　in　winter,　fall,　spring,　and　summer,　respectively;　and　(6)　in　general,　there　is　a　good　positive　correlation　between　the　regional　contribution　and　PM2.5　concentration　in　Beijing.　Specifically,　when　the　regional　transport　contribution　is　large,　the　PM2.5　concentration　tends　to　be　higher.　This　is　especially　true　during　years　when　both　the　concentration　and　contribution　deviate　significantly　from　the　historical　average.