This　study　examines　how　the　COVID-19　pandemic　crisis　affects　the　interactions　between　the　stock,　oil,　gold,　currency,　and　cryptocurrency　markets.　The　impacts　of　the　COVID-19　pandemic　crisis　on　the　optimal　asset　allocation　and　optimal　hedged　strategy　are　also　discussed.　Empirical　results　show　that　the　volatility　spillover　significantly　exists　in　most　of　the　ten　paired　markets　whereas　the　return　spillover　and　correlation　are　significant　only　for　the　few　paired　markets.　Moreover,　the　impact　of　the　COVID-19　pandemic　on　the　return　spillover　is　the　greatest　followed　by　the　correlation　whereas　the　volatility　spillover　is　not　affected　by　the　COVID-19　pandemic.　Furthermore,　the　Quantitative　easing　(QE)　implemented　after　the　COVID-19　pandemic　crisis　increases　the　risk-adjusted　return　for　each　asset　and　minimum　variance　portfolio　(MVP)　and　raises　the　correlation　between　two　assets.　In　addition,　most　of　the　pairs　of　assets　are　not　suitable　to　hedge　each　other　except　for　a　few　pairs　of　assets.　Regarding　these　few　pairs　of　assets,　the　optimal　hedge　asset　with　the　fewer　hedge　cost　is　accompanied　by　less　risk　reduction　and　vice　versa.　Finally,　the　investors　should　choose　the　euro　to　construct　a　portfolio　to　achieve　risk　diversification　and　to　hedge　gold　or　WTI　to　get　the　risk　reduction.　The　above　findings　can　help　investors　and　fund　managers　make　a　useful　investment　strategy,　optimal　asset　allocation,　and　effective　hedged　strategy.　For　example,　the　investors　can　use　the　volatility　of　one　market　to　predict　the　volatility　of　another　market　and　they　can　take　a　long　position　during　the　post-COVID-19　period　but　they　should　withdraw　capital　from　the　market　when　the　QE　tapering　is　executed.　JEL　classificationC52;　C53;　G15.