I'm developing a flash game and i want to put it in Facebook ,My question is the Proper maximum size for it. 500 KB 1 MB ??
I'm taking you to mean .swf size, for loading vs presentation?
I found this link finding the average sizes for flash files. Most seem to be 1MB-5MB. As long as you have a decent loading screen that keeps people attracted, and it's not too much of a wait, then it'll be fine.
On Facebook, everyone's bored. :P