If excel  doesn't provide what you want, then you might be out of luck.
AFAIK there is no user-accessible hover event in Excel.

I'm not sure how a tooltip would work for the contents of a combo  box
anyway. If you hovered over it, it would not know which data row to
display.

It is possible to trap the mouse  movement/position event and you could do
something with that - with significant effort. A Google search for "excel
hover event" found at least one hit for someone trying to do this.

I don't think you can get the tool  tip to change as you
"hover" over an entry. You'll have to actually select it.
then you can use the value to change the ControlTitText property.

Thanks for the response.i'll check with the ControlTitText
property.But in my excel  user wants to see the the name in comobobox and then
select it.He is not able to see the total name as it is longer than
combobox,hence he is expecting Tool tip.