I have a ExtJS panel inside a viewport center region. I want to hide the title of the panel. How can I do it? I\'m using xtype config for declaring the panel.         
        
Use preventHeader property. I checked it and it's worked
See example below
Ext.widget('panel', {
        title: 'Panel header will not be shown',
        preventHeader: true,
        width: 300
    });
You can just use the config
Ext.panel.Panel({
    // title: 'Test',   to neglet this
    header:false,
    tools: [{
        type: 'refresh'
    }, {
        type: 'help'
    }],
});
"header:false config documentation"
Use either the header or headerAsText config option of panel to hide its title. From ExtJS API documentation:
header : Boolean
true to create the Panel's header element explicitly, false to skip creating it. If a title is set the header will be created automatically, otherwise it will not. If a title is set but header is explicitly set to false, the header will not be rendered.
and
headerAsText : Boolean
true to display the panel title in the header, false to hide it (defaults to true).