Occupants’　interactions　with　windows　have　a　significant　influence　on　indoor　air　quality,　thermal　comfort,　and　energy　consumption.　In　residential　buildings,　window　opening　duration　may　vary　considerably　owing　to　different　indoor　and　outdoor　environmental　parameters　and　personal　habits.　In　order　to　investigate　whether　outdoor　PM2.5　affects　human　window　opening　duration,　field　measurements　were　conducted　in　14　residential　buildings　to　monitor　switch　status　of　windows　in　living　room,　bedroom,　and　kitchen.　The　results　showed　that　most　occupants　showed　a　clear　difference　in　window　opening　duration　among　the　three　main　functional　rooms　in　terms　of　the　effect　of　outdoor　PM2.5.　The　heavy　pollution　in　the　non-smog　season　had　a　great　impact　on　occupants’　windowing　behavior,　which　reflects　that　people　did　not　pay　enough　attention　to　the　mild　and　moderate　pollution　in　the　non-smog　season.　Combined　with　the　effects　of　outdoor　PM2.5,　the　bedroom　was　the　best　room　for　the　window　opening　mode.　This　study　reflects　unreasonable　window　opening　situation　in　the　living　room　and　kitchen　currently.　©　2020,　Springer　Nature　Singapore　Pte　Ltd.