As given by Qt's doc from http://qt-project.org/doc/qt-5.1/qmake/qmake-precompiledheaders.html :

to ensure the creation and use of the precompiled header file. You do not need to include the precompiled header file in HEADERS, as qmake will do this if the configuration supports precompiled headers.

However, in Qt Creator, if I remove the entry in HEADERS from .pro file, that header will not show up in the project.