Since ()s are metachars for a regexp, you're actually matching "text1_Right" - which doesn't exist in your example. What you'll have to do is escape the ()s in your string:

@array = ("text1_(Right):662:19990913:662:19990913:1",
"text2(Right):8000:20020116:8000:20020116:1",
"text3:6800:20021015:6900:20021014:1");

$Symbol= "text1_(Right)";

foreach $item (@array){
   if ($item =~ m/\Q$Symbol/i) {
    print "$item\n";
  } 
}
[download]

See perlop for the use of \Q

-- Dan