Compressing Movie problem in Adobe Premiere Pro...

Well, sorry for asking noob questions
(While I'm just a Beginner too~)

Actually, I'm using Adobe Premiere 2.0.
When I import a 5MB 4min mp3 format song,

and immediately Export Movie, no matter if I add ANY frame or not...the MB when exported is...700MB.....

Therefore, I solely believe there is a way to retain it current MB with original Sound unchanged.... hm... could anyone be kind enough to help answer my Question??

~Thanks in Advance~~