Heating　and　cooling　loads　in　residential　buildings　are　determined　not　only　by　outdoor　environment　and　internal　heat　gains,　but　also　by　the　use　of　air　conditioners.　The　usage　includes　the　operation　pattern　of　air　conditioner　and　the　two　set　points　of　room　air　temperature.　One　set　point　is　the　lower　temperature　limit　for　air　conditioner　to　start　up;　the　other　set　point　is　the　upper　temperature　limit　of　the　comfortable　zone　with　air-conditioning.　This　paper　presents　the　investigation　results　of　the　use　of　air　conditioners　in　42　air-conditioned　residential　units　in　Beijing..　It　is　found　that　air　conditioners　are　usually　used　intermittently　in　residential　units.　Occupants　perceive　the　warmth　as　being　less　serve　in　non-air-conditioned　environment　than　in　air-conditioned　environment.　For　most　of　occupants,　they　start　their　air-conditioners　under　the　condition　of　air　temperature　above　29　degrees　C,　while　they　will　not　be　satisfied　with　the　temperature　condition　above　26　degrees　C　in　air-conditioned　environment.