Hi,
You can provide a little more detail, Query may be.
But one thing which you can check straight away is textbox properties in SSRS.
Right click on textbook, go to 'Textbox Properties' and in the Number tab, Select 'Number' and decimal places to be, say 2 or 3.
Check this if works. Though there could be many other reason eg NULL value somehow coming in the Query, Null appears as blank.
Athar.