"http://" prefix is automatically added by the Insert Hyperlink Dialog when the provided URI is to local path or mapped drive, e.g. "Z:\temp". Workaround 1: Set HyperlinkPattern to something that matches file paths, e.g.: (this.radRichTextBox.InsertHyperlinkDialog as RadInsertHyperlinkDialog).HyperlinkPattern = ".*"; Workaround 2: Insert such paths with the "file://" prefix.