Is it possible to change font size in all text boxes at once?

You can try to select all texts and change their height in the Properties windows (Ctrl+1) or use a text style with a fixed font size.

Thank you Vladimir but I have million text boxes that I have to select, that's mine biggest problem.

I hope that you already know this, but I think the Filter command will help you to select more precisely from the drawing.

[QUOTE=VukMorski]Is it possible to change font size in all text boxes at once?
[/QUOTE] If you have creating all text boxes in a layer only. Turn off all other layers and as selecting options choose all. If not choose the option by srinivas.  Arben.Allaraj2008-09-22 11:50:43

One command can help you i.e. type SCALETEXT in command window than select all text and press enter key then give your required height to the text and again press enter.