i'm using richtextbox,

Itcan be stored as text datatype. I am not sure about RTF if it is unicode, then you need to store it as ntext.

If you want to save the text including the formatting you can retrieve it from the RichTextBox.Rtf property.

what should be the datatype for a rtf?

Itcan be stored as text datatype. I am not sure about RTF if it is unicode, then you need to store it as ntext.

i'm using a text datatype and it's working fine. how will i know if it's a unicode?

Unicode is a format to store characters that can not be represented by one byte and therefor has 2 bytes for each character.

http://www.unicode.org/

I have not really looked into RTF or how it works but I did a small test. I created a new document in wordpad and added some characters using the character map tool. I studied the saved RTF document and it is all stored asregular ASCIItext. Itencodes characters outside the regular set.