Thank you for your inquiry.
By default there are no borders inside the grid of the RadCalendar. The appearance you described is a result from any customizations you have applied.
I suggest that you check the CalendarButtonStyle - i.e. the style which is applied to the Day Button and verify that there is no Border set in the style.
If you need further assistance, please send us a sample including your own customizations, so that we may be able to identify where the problem is.
the Telerik team
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