How to remove the default border radius ,Select2

You can add this css :

[class^='select2'] {
  border-radius: 0px !important;
}

fiddle : http://jsfiddle.net/jEADR/1537/

Well I've just tried to do a trick basically in jquery as below and yea it works!!

Execute below 2 lines once you initialize your select2

$('.select2-selection').css('border-radius','0px')
$('.select2-container').children().css('border-radius','0px')