This　paper　investigates　the　impact　of　the　US-China　Trade　War　on　co-movements　between　US　and　Chinese　stock　markets.　It　particularly　examines　the　time-varying　stock　market　co-movement　between　the　United　States　and　China　at　market　level,　as　well　as　at　sector　level,　over　the　period　from　3rd　January　2017　to　23rd　January　2020.　The　＇event　study＇　analysis　is　employed　to　investigate　the　effect　of　US-China　trade　disputes　news　on　co-movement　dynamics,　and　the　news　announcement　effects　before　and　after　the　official　start　of　the　US-China　Trade　War　(regarded　as　6th　July　2018)　are　examined　separately　in　light　of　this　phenomenon.　We　also　identify　structural　breaks　and　spillover　patterns　of　cross-market　co-movements　during　different　phases.　The　results　indicate　that　co-movements　amongst　mainland　China,　Hong　Kong　and　US　stock　markets　are　positively　affected　by　news　releases　and,　after　6th　July　2018,　are　enhanced　significantly.　More　precisely,　there　is　also　empirical　evidence　of　positive　announcement　effects　in　stock　market　co-movements　between　the　US　and　mainland　China　in　specific　sectors　(particularly,　Industrials　and　Information　Technology).　For　international　investors,　this　evidence　suggests　that　the　US-China　Trade　War　has　reduced　the　benefit　of　portfolio　diversification　in　managing　risk.