Two　typical　in-use　diesel　buses　meeting　＇China　IV＇　emission　standard　were　selected　to　do　on-road　emission　tests　using　a　portable　emission　measurement　system　in　Beijing.　The　road　distance　of　testing　was　51.3　km,　the　time　of　testing　was　10　645　s,　and　10　645　data　groups　were　obtained　of　the　buses.　The　running　cycle　in　the　testing　can　typically　reflect　the　real　on-road　running　cycle.　The　emission　factors　of　the　tested　buses　are　(11.02±1.46),　(1.44±0.12),　(0.038±0.01),　and　(0.053±0.03)　g/km　for　NOx,　CO,　total　carbureted　hydrogen　(THC),　and　particulate　matter　(PM),　respectively.　Results　show　that　fuel　consumption　and　pollutant　emission　are　strongly　related　to　the　speed　and　acceleration　in　the　driving　cycles.　Higher　pollutant　emission　rates　and　fuel　consumption　are　tested　during　the　high　speed　and　acceleration　zone　in　the　driving　cycles.　Higher　NOx　emission　rates　are　mainly　during　the　high　speed　and　acceleration　zone.　Higher　CO　emission　rates　are　mainly　during　the　vehicle　speed　exceeding　30　km/h　or　during　the　acceleration　zone.　Higher　THC　emission　rates　were　mainly　during　acceleration　zone　while　the　vehicle　speed　was　slower　than　30　km/h.