bool isMan = false; bool isWoman = false; Center( child: Row( children: [ Padding( padding: EdgeInsets.only(right: 10), child: Text( "Man:", style: TextStyle(color: Colors.white, fontSize: 20), ), ), Theme( data: ThemeData(unselectedWidgetColor: Colors.white), child: Checkbox( value: isMan, checkColor: Color(0xfff44336), activeColor: Colors.white, onChanged: (value) { setState( () { isMan = value!; isWoman = false; }, ); }, ), ), Text( "Woman:", style: TextStyle(color: Colors.white, fontSize: 20), ), Theme( data: ThemeData(unselectedWidgetColor: Colors.white), child: Checkbox( value: isWoman, checkColor: Color(0xfff44336), activeColor: Colors.white, onChanged: (value) { setState( () { isWoman = value!; isMan = false; }, ); }, ), ), ], ), )`

Here is the solution.

bool isMan = false; bool isWoman = false;
Center( child: Row( children: [ Padding( padding: EdgeInsets.only(right: 10), child: Text( "Man:", style: TextStyle(color: Colors.white, fontSize: 20), ), ), Theme( data: ThemeData(unselectedWidgetColor: Colors.white), child: Checkbox( value: isMan, checkColor: Color(0xfff44336), activeColor: Colors.white, onChanged: (value) { setState( () { isMan = value!; isWoman = false; }, ); }, ), ), Text( "Woman:", style: TextStyle(color: Colors.white, fontSize: 20), ), Theme( data: ThemeData(unselectedWidgetColor: Colors.white), child: Checkbox( value: isWoman, checkColor: Color(0xfff44336), activeColor: Colors.white, onChanged: (value) { setState( () { isWoman = value!; isMan = false; }, ); }, ), ), ], ), )