I want to open a window using "window.open()" function which has NO TITLE BAR, but it is working if i am opening my window in maximize format.
But if i am trying to open the window with specified size, the TITLE BAR remain there.

The titlebar is something you cannot remove cross-browser.
It is really part of the operating system rather than the Web browser and client-side Javascript should not be able to affect that.

Using the fullscreen property will create a window that does not have a titlebar, but that is an IE feature.