Hi there

I've installed KDE on Ubuntu (switch between them via logout & session) but the font in KDE environment has changed to Gnome default font.Even the font of some kde-related programs (such as amarok,kchmviewer,etc) which were installed on gnome before this time has been changed to gnome font.I tried to fix this via KDE control center but it had no result.
How can I retrieve kde default font in its own environment?

thanks in advance

What do you mean "gnome default font" and "kde default font" ?
Can you explain precisely :
?

Apparently, the default font for gnome is Sans (regular) & for KDE is Sans Serif (regular) but the latter seems bolder than the former.

As I told before the font on my KDE environment has been changed & resembled to the font we can see on gnome (become thinner).I checked the font regulations in KDE control center but everything was OK (set according the default setting).I even changed the font to Sans Serif Bold but it seemed different from what was at KDE startup.

Moreover, in Font installer part of KDE control center after pressing the Administrator Mode button the font of that part is changed to default quality.This matter can be seen in every part of control center which has Administrator Mode such as Login Manager.

Sorry I don't use Ubuntu and I don't know if installing KDE in Ubuntu is good regarding fonts, rather than installing Kubuntu, which should be better configured for KDE.
Maybe ask a Ubuntu forum or wait for another answer here.
Good luck.