I'm not sure what you did but the script you show can't work.

str_replace takes three arguments and you have to use "\\" and not "\".

oops, i am sorry, yes i know it takes three arguments, i used following script

print str_replace('\\',"/","wwwroot\test\wp2");

It's still bogus. do an 
echo "wwwroot\test\wp2";

and you'll see why (\t is a <tab>, you need to escape it properly if you don't want to have a tab there. If you do, your replace will work as you expect it.). str_replace works correctly and as intended. The bug is in your understanding, not the engine.

I guess it becuase of escape sequence,
as wwwroot\test\wp has \t in it, I also tried other strings like wwwroot\nest\wp, it also produce same result
and when i put an extra slash wwwroot\\test\wp then it gives me good result

Ok, but when i use
echo addslashes("wwwroot\test\wp");
it still prints wwwroot est\\wp

so even if use following 
$url= addslashes("wwwroot\test\wp");
echo str_replace("\\","/",$url);

I would have put an exta slash if knew the string always :), since it is variable, i am be having problem at undersating, but i am getting my expected results using str_replace();

Thanks

Please stop using the bugs system for these kinds of problems. that's NOT what it is for. If you need help understanding what you're doing wrong, check out the php.general mailinglist or any other of the links here: http://www.php.net/support.php