For a data validation dropdown list, you can't change the font size.
There are a couple of workarounds he

http://www.contextures.com/xlDataVal08.html#Font

Or, there's a sample file here that provides a combobox from which you
can select one of the values from the data validation list. In the
combobox, you can change the font size:

http://www.contextures.com/excelfiles.html

jc wrote:
i have created several drop-down lists using the data/validate function in
Excel, but the font / size of the list items in the drop-down list are too
small to read...


--
Debra Dalgleish
Excel FAQ, Tips & Book List
http://www.contextures.com/tiptech.html