The　urban　spatial　expansion　has　led　to　the　considerable　substitution　of　natural　vegetation-dominated　land　surfaces　by　impervious　surfaces,　especially　in　large　cities,　with　great　impacts　on　urban　ecological　quality.　Two　most　heavily　populated　cities,　Shanghai　of　China　and　New　York　of　USA,　were　chosen　as　the　study　cases.　Based　on　Landsat　images　obtained　in　1989,　2002,　2015　in　Shanghai　and　in　1991,　2001,　2015　in　New　York,　normalized　difference　impervious　surface　index　(NDISI)　was　used　to　extract　impervious　surface　(IS)　information.　The　remote　sensing　based　ecological　index　(RSEI)　was　then　applied　to　evaluate　the　changes　of　urban　ecological　quality　caused　by　the　increased　impervious　surface.　Furthermore,　landscape　pattern　indices　were　used　to　analyze　the　differences　of　spatial　structure　of　impervious　surface　between　Shanghai　and　New　York　and　their　influences　on　urban　ecological　quality.　The　results　showed　a　significant　difference　in　urban　expansion　rate　and　pattern　between　Shanghai　and　New　York　from　the　early　1990s　to　2015.　The　IS　expansion　area　in　Shanghai　was　17.4　times　as　much　as　that　in　New　York.　The　annual　IS　increase　rate　of　Shanghai　was　62.2　times　as　much　as　that　of　New　York.　Shanghai　had　experienced　an　expansion　from　urban　center　to　the　surrounding　countryside　in　a　concentric　ring　pattern,　whereas　New　York　showed　no　much　expansion　but　had　IS　increase　mainly　within　the　inner　city　through　space　filling　pattern.　These　differences　in　IS　change　rate　and　spatial　distribution　pattern　had　resulted　in　the　difference　in　urban　ecological　quality　of　the　two　cities.　The　mean　RSEI　in　Shanghai　dropped　from　0.717　in　1989　to　0.453　in　2015,　with　a　decrease　of　36.8%.　In　contrast,　the　RSEI　of　New　York　had　a　decline　of　6.9%　from　0.552　in　1991　to　0.514　in　2015.　The　poor　ecological　condition　urban　area　tended　to　have　large　IS　patches　that　were　well　connected　and　aggregated.　©　2018,　Science　Press.　All　right　reserved.